Skip to content

L
linux
Commit dde79789 authored by Rusty Russell's avatar Rusty Russell Committed by Linus Torvalds
Browse files
Options

lguest: documentation IV: Launcher 

Documentation: The Launcher
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e2c97843
Hide whitespace changes
Inline Side-by-side
Showing with 982 additions and 72 deletions
Documentation/lguest/lguest.c
View file @ dde79789
......@@ -34,12 +34,20 @@
#include <termios.h>
#include <getopt.h>
#include <zlib.h>
/*L:110 We can ignore the 28 include files we need for this program, but I do
* want to draw attention to the use of kernel-style types.
*
* As Linus said, "C is a Spartan language, and so should your naming be." I
* like these abbreviations and the header we need uses them, so we define them
* here.
*/
typedef unsigned long long u64;
typedef uint32_t u32;
typedef uint16_t u16;
typedef uint8_t u8;
#include "../../include/linux/lguest_launcher.h"
#include "../../include/asm-i386/e820.h"
/*:*/
#define PAGE_PRESENT 0x7 /* Present, RW, Execute */
#define NET_PEERNUM 1
......@@ -48,33 +56,52 @@ typedef uint8_t u8;
#define SIOCBRADDIF 0x89a2 /* add interface to bridge */
#endif
/*L:120 verbose is both a global flag and a macro. The C preprocessor allows
* this, and although I wouldn't recommend it, it works quite nicely here. */
static bool verbose;
#define verbose(args...) \
do { if (verbose) printf(args); } while(0)
/*:*/
/* The pipe to send commands to the waker process */
static int waker_fd;
/* The top of guest physical memory. */
static u32 top;
/* This is our list of devices. */
struct device_list
{
/* Summary information about the devices in our list: ready to pass to
* select() to ask which need servicing.*/
fd_set infds;
int max_infd;
/* The descriptor page for the devices. */
struct lguest_device_desc *descs;
/* A single linked list of devices. */
struct device *dev;
/* ... And an end pointer so we can easily append new devices */
struct device **lastdev;
};
/* The device structure describes a single device. */
struct device
{
/* The linked-list pointer. */
struct device *next;
/* The descriptor for this device, as mapped into the Guest. */
struct lguest_device_desc *desc;
/* The memory page(s) of this device, if any. Also mapped in Guest. */
void *mem;
/* Watch this fd if handle_input non-NULL. */
/* If handle_input is set, it wants to be called when this file
* descriptor is ready. */
int fd;
bool (*handle_input)(int fd, struct device *me);
/* Watch DMA to this key if handle_input non-NULL. */
/* If handle_output is set, it wants to be called when the Guest sends
* DMA to this key. */
unsigned long watch_key;
u32 (*handle_output)(int fd, const struct iovec *iov,
unsigned int num, struct device *me);
......@@ -83,6 +110,11 @@ struct device
void *priv;
};
/*L:130
* Loading the Kernel.
*
* We start with couple of simple helper routines. open_or_die() avoids
* error-checking code cluttering the callers: */
static int open_or_die(const char *name, int flags)
{
int fd = open(name, flags);
......@@ -91,26 +123,38 @@ static int open_or_die(const char *name, int flags)
return fd;
}
/* map_zeroed_pages() takes a (page-aligned) address and a number of pages. */
static void *map_zeroed_pages(unsigned long addr, unsigned int num)
{
/* We cache the /dev/zero file-descriptor so we only open it once. */
static int fd = -1;
if (fd == -1)
fd = open_or_die("/dev/zero", O_RDONLY);
/* We use a private mapping (ie. if we write to the page, it will be
* copied), and obviously we insist that it be mapped where we ask. */
if (mmap((void *)addr, getpagesize() * num,
PROT_READ|PROT_WRITE|PROT_EXEC, MAP_FIXED|MAP_PRIVATE, fd, 0)
!= (void *)addr)
err(1, "Mmaping %u pages of /dev/zero @%p", num, (void *)addr);
/* Returning the address is just a courtesy: can simplify callers. */
return (void *)addr;
}
/* Find magic string marking entry point, return entry point. */
/* To find out where to start we look for the magic Guest string, which marks
* the code we see in lguest_asm.S. This is a hack which we are currently
* plotting to replace with the normal Linux entry point. */
static unsigned long entry_point(void *start, void *end,
unsigned long page_offset)
{
void *p;
/* The scan gives us the physical starting address. We want the
* virtual address in this case, and fortunately, we already figured
* out the physical-virtual difference and passed it here in
* "page_offset". */
for (p = start; p < end; p++)
if (memcmp(p, "GenuineLguest", strlen("GenuineLguest")) == 0)
return (long)p + strlen("GenuineLguest") + page_offset;
......@@ -118,7 +162,17 @@ static unsigned long entry_point(void *start, void *end,
err(1, "Is this image a genuine lguest?");
}
/* Returns the entry point */
/* This routine takes an open vmlinux image, which is in ELF, and maps it into
* the Guest memory. ELF = Embedded Linking Format, which is the format used
* by all modern binaries on Linux including the kernel.
*
* The ELF headers give *two* addresses: a physical address, and a virtual
* address. The Guest kernel expects to be placed in memory at the physical
* address, and the page tables set up so it will correspond to that virtual
* address. We return the difference between the virtual and physical
* addresses in the "page_offset" pointer.
*
* We return the starting address. */
static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
unsigned long *page_offset)
{
......@@ -127,40 +181,61 @@ static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
unsigned int i;
unsigned long start = -1UL, end = 0;
/* Sanity checks. */
/* Sanity checks on the main ELF header: an x86 executable with a
* reasonable number of correctly-sized program headers. */
if (ehdr->e_type != ET_EXEC
|| ehdr->e_machine != EM_386
|| ehdr->e_phentsize != sizeof(Elf32_Phdr)
|| ehdr->e_phnum < 1 || ehdr->e_phnum > 65536U/sizeof(Elf32_Phdr))
errx(1, "Malformed elf header");
/* An ELF executable contains an ELF header and a number of "program"
* headers which indicate which parts ("segments") of the program to
* load where. */
/* We read in all the program headers at once: */
if (lseek(elf_fd, ehdr->e_phoff, SEEK_SET) < 0)
err(1, "Seeking to program headers");
if (read(elf_fd, phdr, sizeof(phdr)) != sizeof(phdr))
err(1, "Reading program headers");
/* We don't know page_offset yet. */
*page_offset = 0;
/* We map the loadable segments at virtual addresses corresponding
* to their physical addresses (our virtual == guest physical). */
/* Try all the headers: there are usually only three. A read-only one,
* a read-write one, and a "note" section which isn't loadable. */
for (i = 0; i < ehdr->e_phnum; i++) {
/* If this isn't a loadable segment, we ignore it */
if (phdr[i].p_type != PT_LOAD)
continue;
verbose("Section %i: size %i addr %p\n",
i, phdr[i].p_memsz, (void *)phdr[i].p_paddr);
/* We expect linear address space. */
/* We expect a simple linear address space: every segment must
* have the same difference between virtual (p_vaddr) and
* physical (p_paddr) address. */
if (!*page_offset)
*page_offset = phdr[i].p_vaddr - phdr[i].p_paddr;
else if (*page_offset != phdr[i].p_vaddr - phdr[i].p_paddr)
errx(1, "Page offset of section %i different", i);
/* We track the first and last address we mapped, so we can
* tell entry_point() where to scan. */
if (phdr[i].p_paddr < start)
start = phdr[i].p_paddr;
if (phdr[i].p_paddr + phdr[i].p_filesz > end)
end = phdr[i].p_paddr + phdr[i].p_filesz;
/* We map everything private, writable. */
/* We map this section of the file at its physical address. We
* map it read & write even if the header says this segment is
* read-only. The kernel really wants to be writable: it
* patches its own instructions which would normally be
* read-only.
*
* MAP_PRIVATE means that the page won't be copied until a
* write is done to it. This allows us to share much of the
* kernel memory between Guests. */
addr = mmap((void *)phdr[i].p_paddr,
phdr[i].p_filesz,
PROT_READ|PROT_WRITE|PROT_EXEC,
......@@ -174,7 +249,31 @@ static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
return entry_point((void *)start, (void *)end, *page_offset);
}
/* This is amazingly reliable. */
/*L:170 Prepare to be SHOCKED and AMAZED. And possibly a trifle nauseated.
*
* We know that CONFIG_PAGE_OFFSET sets what virtual address the kernel expects
* to be. We don't know what that option was, but we can figure it out
* approximately by looking at the addresses in the code. I chose the common
* case of reading a memory location into the %eax register:
*
* movl <some-address>, %eax
*
* This gets encoded as five bytes: "0xA1 <4-byte-address>". For example,
* "0xA1 0x18 0x60 0x47 0xC0" reads the address 0xC0476018 into %eax.
*
* In this example can guess that the kernel was compiled with
* CONFIG_PAGE_OFFSET set to 0xC0000000 (it's always a round number). If the
* kernel were larger than 16MB, we might see 0xC1 addresses show up, but our
* kernel isn't that bloated yet.
*
* Unfortunately, x86 has variable-length instructions, so finding this
* particular instruction properly involves writing a disassembler. Instead,
* we rely on statistics. We look for "0xA1" and tally the different bytes
* which occur 4 bytes later (the "0xC0" in our example above). When one of
* those bytes appears three times, we can be reasonably confident that it
* forms the start of CONFIG_PAGE_OFFSET.
*
* This is amazingly reliable. */
static unsigned long intuit_page_offset(unsigned char *img, unsigned long len)
{
unsigned int i, possibilities[256] = { 0 };
......@@ -187,30 +286,52 @@ static unsigned long intuit_page_offset(unsigned char *img, unsigned long len)
errx(1, "could not determine page offset");
}
/*L:160 Unfortunately the entire ELF image isn't compressed: the segments
* which need loading are extracted and compressed raw. This denies us the
* information we need to make a fully-general loader. */
static unsigned long unpack_bzimage(int fd, unsigned long *page_offset)
{
gzFile f;
int ret, len = 0;
/* A bzImage always gets loaded at physical address 1M. This is
* actually configurable as CONFIG_PHYSICAL_START, but as the comment
* there says, "Don't change this unless you know what you are doing".
* Indeed. */
void *img = (void *)0x100000;
/* gzdopen takes our file descriptor (carefully placed at the start of
* the GZIP header we found) and returns a gzFile. */
f = gzdopen(fd, "rb");
/* We read it into memory in 64k chunks until we hit the end. */
while ((ret = gzread(f, img + len, 65536)) > 0)
len += ret;
if (ret < 0)
err(1, "reading image from bzImage");
verbose("Unpacked size %i addr %p\n", len, img);
/* Without the ELF header, we can't tell virtual-physical gap. This is
* CONFIG_PAGE_OFFSET, and people do actually change it. Fortunately,
* I have a clever way of figuring it out from the code itself. */
*page_offset = intuit_page_offset(img, len);
return entry_point(img, img + len, *page_offset);
}
/*L:150 A bzImage, unlike an ELF file, is not meant to be loaded. You're
* supposed to jump into it and it will unpack itself. We can't do that
* because the Guest can't run the unpacking code, and adding features to
* lguest kills puppies, so we don't want to.
*
* The bzImage is formed by putting the decompressing code in front of the
* compressed kernel code. So we can simple scan through it looking for the
* first "gzip" header, and start decompressing from there. */
static unsigned long load_bzimage(int fd, unsigned long *page_offset)
{
unsigned char c;
int state = 0;
/* Ugly brute force search for gzip header. */
/* GZIP header is 0x1F 0x8B <method> <flags>... <compressed-by>. */
while (read(fd, &c, 1) == 1) {
switch (state) {
case 0:
......@@ -227,8 +348,10 @@ static unsigned long load_bzimage(int fd, unsigned long *page_offset)
state++;
break;
case 9:
/* Seek back to the start of the gzip header. */
lseek(fd, -10, SEEK_CUR);
if (c != 0x03) /* Compressed under UNIX. */
/* One final check: "compressed under UNIX". */
if (c != 0x03)
state = -1;
else
return unpack_bzimage(fd, page_offset);
......@@ -237,25 +360,43 @@ static unsigned long load_bzimage(int fd, unsigned long *page_offset)
errx(1, "Could not find kernel in bzImage");
}
/*L:140 Loading the kernel is easy when it's a "vmlinux", but most kernels
* come wrapped up in the self-decompressing "bzImage" format. With some funky
* coding, we can load those, too. */
static unsigned long load_kernel(int fd, unsigned long *page_offset)
{
Elf32_Ehdr hdr;
/* Read in the first few bytes. */
if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr))
err(1, "Reading kernel");
/* If it's an ELF file, it starts with "\177ELF" */
if (memcmp(hdr.e_ident, ELFMAG, SELFMAG) == 0)
return map_elf(fd, &hdr, page_offset);
/* Otherwise we assume it's a bzImage, and try to unpack it */
return load_bzimage(fd, page_offset);
}
/* This is a trivial little helper to align pages. Andi Kleen hated it because
* it calls getpagesize() twice: "it's dumb code."
*
* Kernel guys get really het up about optimization, even when it's not
* necessary. I leave this code as a reaction against that. */
static inline unsigned long page_align(unsigned long addr)
{
/* Add upwards and truncate downwards. */
return ((addr + getpagesize()-1) & ~(getpagesize()-1));
}
/* initrd gets loaded at top of memory: return length. */
/*L:180 An "initial ram disk" is a disk image loaded into memory along with
* the kernel which the kernel can use to boot from without needing any
* drivers. Most distributions now use this as standard: the initrd contains
* the code to load the appropriate driver modules for the current machine.
*
* Importantly, James Morris works for RedHat, and Fedora uses initrds for its
* kernels. He sent me this (and tells me when I break it). */
static unsigned long load_initrd(const char *name, unsigned long mem)
{
int ifd;
......@@ -264,21 +405,35 @@ static unsigned long load_initrd(const char *name, unsigned long mem)
void *iaddr;
ifd = open_or_die(name, O_RDONLY);
/* fstat() is needed to get the file size. */
if (fstat(ifd, &st) < 0)
err(1, "fstat() on initrd '%s'", name);
/* The length needs to be rounded up to a page size: mmap needs the
* address to be page aligned. */
len = page_align(st.st_size);
/* We map the initrd at the top of memory. */
iaddr = mmap((void *)mem - len, st.st_size,
PROT_READ|PROT_EXEC|PROT_WRITE,
MAP_FIXED|MAP_PRIVATE, ifd, 0);
if (iaddr != (void *)mem - len)
err(1, "Mmaping initrd '%s' returned %p not %p",
name, iaddr, (void *)mem - len);
/* Once a file is mapped, you can close the file descriptor. It's a
* little odd, but quite useful. */
close(ifd);
verbose("mapped initrd %s size=%lu @ %p\n", name, st.st_size, iaddr);
/* We return the initrd size. */
return len;
}
/* Once we know how much memory we have, and the address the Guest kernel
* expects, we can construct simple linear page tables which will get the Guest
* far enough into the boot to create its own.
*
* We lay them out of the way, just below the initrd (which is why we need to
* know its size). */
static unsigned long setup_pagetables(unsigned long mem,
unsigned long initrd_size,
unsigned long page_offset)
......@@ -287,23 +442,32 @@ static unsigned long setup_pagetables(unsigned long mem,
unsigned int mapped_pages, i, linear_pages;
unsigned int ptes_per_page = getpagesize()/sizeof(u32);
/* If we can map all of memory above page_offset, we do so. */
/* Ideally we map all physical memory starting at page_offset.
* However, if page_offset is 0xC0000000 we can only map 1G of physical
* (0xC0000000 + 1G overflows). */
if (mem <= -page_offset)
mapped_pages = mem/getpagesize();
else
mapped_pages = -page_offset/getpagesize();
/* Each linear PTE page can map ptes_per_page pages. */
/* Each PTE page can map ptes_per_page pages: how many do we need? */
linear_pages = (mapped_pages + ptes_per_page-1)/ptes_per_page;
/* We lay out top-level then linear mapping immediately below initrd */
/* We put the toplevel page directory page at the top of memory. */
pgdir = (void *)mem - initrd_size - getpagesize();
/* Now we use the next linear_pages pages as pte pages */
linear = (void *)pgdir - linear_pages*getpagesize();
/* Linear mapping is easy: put every page's address into the mapping in
* order. PAGE_PRESENT contains the flags Present, Writable and
* Executable. */
for (i = 0; i < mapped_pages; i++)
linear[i] = ((i * getpagesize()) | PAGE_PRESENT);
/* Now set up pgd so that this memory is at page_offset */
/* The top level points to the linear page table pages above. The
* entry representing page_offset points to the first one, and they
* continue from there. */
for (i = 0; i < mapped_pages; i += ptes_per_page) {
pgdir[(i + page_offset/getpagesize())/ptes_per_page]
= (((u32)linear + i*sizeof(u32)) | PAGE_PRESENT);
......@@ -312,9 +476,13 @@ static unsigned long setup_pagetables(unsigned long mem,
verbose("Linear mapping of %u pages in %u pte pages at %p\n",
mapped_pages, linear_pages, linear);
/* We return the top level (guest-physical) address: the kernel needs
* to know where it is. */
return (unsigned long)pgdir;
}
/* Simple routine to roll all the commandline arguments together with spaces
* between them. */
static void concat(char *dst, char *args[])
{
unsigned int i, len = 0;
......@@ -328,6 +496,10 @@ static void concat(char *dst, char *args[])
dst[len] = '\0';
}
/* This is where we actually tell the kernel to initialize the Guest. We saw
* the arguments it expects when we looked at initialize() in lguest_user.c:
* the top physical page to allow, the top level pagetable, the entry point and
* the page_offset constant for the Guest. */
static int tell_kernel(u32 pgdir, u32 start, u32 page_offset)
{
u32 args[] = { LHREQ_INITIALIZE,
......@@ -337,8 +509,11 @@ static int tell_kernel(u32 pgdir, u32 start, u32 page_offset)
fd = open_or_die("/dev/lguest", O_RDWR);
if (write(fd, args, sizeof(args)) < 0)
err(1, "Writing to /dev/lguest");
/* We return the /dev/lguest file descriptor to control this Guest */
return fd;
}
/*:*/
static void set_fd(int fd, struct device_list *devices)
{
......@@ -347,61 +522,108 @@ static void set_fd(int fd, struct device_list *devices)
devices->max_infd = fd;
}
/* When input arrives, we tell the kernel to kick lguest out with -EAGAIN. */
/*L:200
* The Waker.
*
* With a console and network devices, we can have lots of input which we need
* to process. We could try to tell the kernel what file descriptors to watch,
* but handing a file descriptor mask through to the kernel is fairly icky.
*
* Instead, we fork off a process which watches the file descriptors and writes
* the LHREQ_BREAK command to the /dev/lguest filedescriptor to tell the Host
* loop to stop running the Guest. This causes it to return from the
* /dev/lguest read with -EAGAIN, where it will write to /dev/lguest to reset
* the LHREQ_BREAK and wake us up again.
*
* This, of course, is merely a different *kind* of icky.
*/
static void wake_parent(int pipefd, int lguest_fd, struct device_list *devices)
{
/* Add the pipe from the Launcher to the fdset in the device_list, so
* we watch it, too. */
set_fd(pipefd, devices);
for (;;) {
fd_set rfds = devices->infds;
u32 args[] = { LHREQ_BREAK, 1 };
/* Wait until input is ready from one of the devices. */
select(devices->max_infd+1, &rfds, NULL, NULL, NULL);
/* Is it a message from the Launcher? */
if (FD_ISSET(pipefd, &rfds)) {
int ignorefd;
/* If read() returns 0, it means the Launcher has
* exited. We silently follow. */
if (read(pipefd, &ignorefd, sizeof(ignorefd)) == 0)
exit(0);
/* Otherwise it's telling us there's a problem with one
* of the devices, and we should ignore that file
* descriptor from now on. */
FD_CLR(ignorefd, &devices->infds);
} else
} else /* Send LHREQ_BREAK command. */
write(lguest_fd, args, sizeof(args));
}
}
/* This routine just sets up a pipe to the Waker process. */
static int setup_waker(int lguest_fd, struct device_list *device_list)
{
int pipefd[2], child;
/* We create a pipe to talk to the waker, and also so it knows when the
* Launcher dies (and closes pipe). */
pipe(pipefd);
child = fork();
if (child == -1)
err(1, "forking");
if (child == 0) {
/* Close the "writing" end of our copy of the pipe */
close(pipefd[1]);
wake_parent(pipefd[0], lguest_fd, device_list);
}
/* Close the reading end of our copy of the pipe. */
close(pipefd[0]);
/* Here is the fd used to talk to the waker. */
return pipefd[1];
}
/*L:210
* Device Handling.
*
* When the Guest sends DMA to us, it sends us an array of addresses and sizes.
* We need to make sure it's not trying to reach into the Launcher itself, so
* we have a convenient routine which check it and exits with an error message
* if something funny is going on:
*/
static void *_check_pointer(unsigned long addr, unsigned int size,
unsigned int line)
{
/* We have to separately check addr and addr+size, because size could
* be huge and addr + size might wrap around. */
if (addr >= top || addr + size >= top)
errx(1, "%s:%i: Invalid address %li", __FILE__, line, addr);
/* We return a pointer for the caller's convenience, now we know it's
* safe to use. */
return (void *)addr;
}
/* A macro which transparently hands the line number to the real function. */
#define check_pointer(addr,size) _check_pointer(addr, size, __LINE__)
/* Returns pointer to dma->used_len */
/* The Guest has given us the address of a "struct lguest_dma". We check it's
* OK and convert it to an iovec (which is a simple array of ptr/size
* pairs). */
static u32 *dma2iov(unsigned long dma, struct iovec iov[], unsigned *num)
{
unsigned int i;
struct lguest_dma *udma;
/* First we make sure that the array memory itself is valid. */
udma = check_pointer(dma, sizeof(*udma));
/* Now we check each element */
for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
/* A zero length ends the array. */
if (!udma->len[i])
break;
......@@ -409,9 +631,15 @@ static u32 *dma2iov(unsigned long dma, struct iovec iov[], unsigned *num)
iov[i].iov_len = udma->len[i];
}
*num = i;
/* We return the pointer to where the caller should write the amount of
* the buffer used. */
return &udma->used_len;
}
/* This routine gets a DMA buffer from the Guest for a given key, and converts
* it to an iovec array. It returns the interrupt the Guest wants when we're
* finished, and a pointer to the "used_len" field to fill in. */
static u32 *get_dma_buffer(int fd, void *key,
struct iovec iov[], unsigned int *num, u32 *irq)
{
......@@ -419,16 +647,21 @@ static u32 *get_dma_buffer(int fd, void *key,
unsigned long udma;
u32 *res;
/* Ask the kernel for a DMA buffer corresponding to this key. */
udma = write(fd, buf, sizeof(buf));
/* They haven't registered any, or they're all used? */
if (udma == (unsigned long)-1)
return NULL;
/* Kernel stashes irq in ->used_len. */
/* Convert it into our iovec array */
res = dma2iov(udma, iov, num);
/* The kernel stashes irq in ->used_len to get it out to us. */
*irq = *res;
/* Return a pointer to ((struct lguest_dma *)udma)->used_len. */
return res;
}
/* This is a convenient routine to send the Guest an interrupt. */
static void trigger_irq(int fd, u32 irq)
{
u32 buf[] = { LHREQ_IRQ, irq };
......@@ -436,6 +669,10 @@ static void trigger_irq(int fd, u32 irq)
err(1, "Triggering irq %i", irq);
}
/* This simply sets up an iovec array where we can put data to be discarded.
* This happens when the Guest doesn't want or can't handle the input: we have
* to get rid of it somewhere, and if we bury it in the ceiling space it will
* start to smell after a week. */
static void discard_iovec(struct iovec *iov, unsigned int *num)
{
static char discard_buf[1024];
......@@ -444,19 +681,24 @@ static void discard_iovec(struct iovec *iov, unsigned int *num)
iov->iov_len = sizeof(discard_buf);
}
/* Here is the input terminal setting we save, and the routine to restore them
* on exit so the user can see what they type next. */
static struct termios orig_term;
static void restore_term(void)
{
tcsetattr(STDIN_FILENO, TCSANOW, &orig_term);
}
/* We associate some data with the console for our exit hack. */
struct console_abort
{
/* How many times have they hit ^C? */
int count;
/* When did they start? */
struct timeval start;
};
/* We DMA input to buffer bound at start of console page. */
/* This is the routine which handles console input (ie. stdin). */
static bool handle_console_input(int fd, struct device *dev)
{
u32 irq = 0, *lenp;
......@@ -465,24 +707,38 @@ static bool handle_console_input(int fd, struct device *dev)
struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
struct console_abort *abort = dev->priv;
/* First we get the console buffer from the Guest. The key is dev->mem
* which was set to 0 in setup_console(). */
lenp = get_dma_buffer(fd, dev->mem, iov, &num, &irq);
if (!lenp) {
/* If it's not ready for input, warn and set up to discard. */
warn("console: no dma buffer!");
discard_iovec(iov, &num);
}
/* This is why we convert to iovecs: the readv() call uses them, and so
* it reads straight into the Guest's buffer. */
len = readv(dev->fd, iov, num);
if (len <= 0) {
/* This implies that the console is closed, is /dev/null, or
* something went terribly wrong. We still go through the rest
* of the logic, though, especially the exit handling below. */
warnx("Failed to get console input, ignoring console.");
len = 0;
}
/* If we read the data into the Guest, fill in the length and send the
* interrupt. */
if (lenp) {
*lenp = len;
trigger_irq(fd, irq);
}
/* Three ^C within one second? Exit. */
/* Three ^C within one second? Exit.
*
* This is such a hack, but works surprisingly well. Each ^C has to be
* in a buffer by itself, so they can't be too fast. But we check that
* we get three within about a second, so they can't be too slow. */
if (len == 1 && ((char *)iov[0].iov_base)[0] == 3) {
if (!abort->count++)
gettimeofday(&abort->start, NULL);
......@@ -490,43 +746,60 @@ static bool handle_console_input(int fd, struct device *dev)
struct timeval now;
gettimeofday(&now, NULL);
if (now.tv_sec <= abort->start.tv_sec+1) {
/* Make sure waker is not blocked in BREAK */
u32 args[] = { LHREQ_BREAK, 0 };
/* Close the fd so Waker will know it has to
* exit. */
close(waker_fd);
/* Just in case waker is blocked in BREAK, send
* unbreak now. */
write(fd, args, sizeof(args));
exit(2);
}
abort->count = 0;
}
} else
/* Any other key resets the abort counter. */
abort->count = 0;
/* Now, if we didn't read anything, put the input terminal back and
* return failure (meaning, don't call us again). */
if (!len) {
restore_term();
return false;
}
/* Everything went OK! */
return true;
}
/* Handling console output is much simpler than input. */
static u32 handle_console_output(int fd, const struct iovec *iov,
unsigned num, struct device*dev)
{
/* Whatever the Guest sends, write it to standard output. Return the
* number of bytes written. */
return writev(STDOUT_FILENO, iov, num);
}
/* Guest->Host network output is also pretty easy. */
static u32 handle_tun_output(int fd, const struct iovec *iov,
unsigned num, struct device *dev)
{
/* Now we've seen output, we should warn if we can't get buffers. */
/* We put a flag in the "priv" pointer of the network device, and set
* it as soon as we see output. We'll see why in handle_tun_input() */
*(bool *)dev->priv = true;
/* Whatever packet the Guest sent us, write it out to the tun
* device. */
return writev(dev->fd, iov, num);
}
/* This matches the peer_key() in lguest_net.c. The key for any given slot
* is the address of the network device's page plus 4 * the slot number. */
static unsigned long peer_offset(unsigned int peernum)
{
return 4 * peernum;
}
/* This is where we handle a packet coming in from the tun device */
static bool handle_tun_input(int fd, struct device *dev)
{
u32 irq = 0, *lenp;
......@@ -534,17 +807,28 @@ static bool handle_tun_input(int fd, struct device *dev)
unsigned num;
struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
/* First we get a buffer the Guest has bound to its key. */
lenp = get_dma_buffer(fd, dev->mem+peer_offset(NET_PEERNUM), iov, &num,
&irq);
if (!lenp) {
/* Now, it's expected that if we try to send a packet too
* early, the Guest won't be ready yet. This is why we set a
* flag when the Guest sends its first packet. If it's sent a
* packet we assume it should be ready to receive them.
*
* Actually, this is what the status bits in the descriptor are
* for: we should *use* them. FIXME! */
if (*(bool *)dev->priv)
warn("network: no dma buffer!");
discard_iovec(iov, &num);
}
/* Read the packet from the device directly into the Guest's buffer. */
len = readv(dev->fd, iov, num);
if (len <= 0)
err(1, "reading network");
/* Write the used_len, and trigger the interrupt for the Guest */
if (lenp) {
*lenp = len;
trigger_irq(fd, irq);
......@@ -552,9 +836,13 @@ static bool handle_tun_input(int fd, struct device *dev)
verbose("tun input packet len %i [%02x %02x] (%s)\n", len,
((u8 *)iov[0].iov_base)[0], ((u8 *)iov[0].iov_base)[1],
lenp ? "sent" : "discarded");
/* All good. */
return true;
}
/* The last device handling routine is block output: the Guest has sent a DMA
* to the block device. It will have placed the command it wants in the
* "struct lguest_block_page". */
static u32 handle_block_output(int fd, const struct iovec *iov,
unsigned num, struct device *dev)
{
......@@ -564,36 +852,64 @@ static u32 handle_block_output(int fd, const struct iovec *iov,
struct iovec reply[LGUEST_MAX_DMA_SECTIONS];
off64_t device_len, off = (off64_t)p->sector * 512;
/* First we extract the device length from the dev->priv pointer. */
device_len = *(off64_t *)dev->priv;
/* We first check that the read or write is within the length of the
* block file. */
if (off >= device_len)
err(1, "Bad offset %llu vs %llu", off, device_len);
/* Move to the right location in the block file. This shouldn't fail,
* but best to check. */
if (lseek64(dev->fd, off, SEEK_SET) != off)
err(1, "Bad seek to sector %i", p->sector);
verbose("Block: %s at offset %llu\n", p->type ? "WRITE" : "READ", off);
/* They were supposed to bind a reply buffer at key equal to the start
* of the block device memory. We need this to tell them when the
* request is finished. */
lenp = get_dma_buffer(fd, dev->mem, reply, &reply_num, &irq);
if (!lenp)
err(1, "Block request didn't give us a dma buffer");
if (p->type) {
/* A write request. The DMA they sent contained the data, so
* write it out. */
len = writev(dev->fd, iov, num);
/* Grr... Now we know how long the "struct lguest_dma" they
* sent was, we make sure they didn't try to write over the end
* of the block file (possibly extending it). */
if (off + len > device_len) {
/* Trim it back to the correct length */
ftruncate(dev->fd, device_len);
/* Die, bad Guest, die. */
errx(1, "Write past end %llu+%u", off, len);
}
/* The reply length is 0: we just send back an empty DMA to
* interrupt them and tell them the write is finished. */
*lenp = 0;
} else {
/* A read request. They sent an empty DMA to start the
* request, and we put the read contents into the reply
* buffer. */
len = readv(dev->fd, reply, reply_num);
*lenp = len;
}
/* The result is 1 (done), 2 if there was an error (short read or
* write). */
p->result = 1 + (p->bytes != len);
/* Now tell them we've used their reply buffer. */
trigger_irq(fd, irq);
/* We're supposed to return the number of bytes of the output buffer we
* used. But the block device uses the "result" field instead, so we
* don't bother. */
return 0;
}
/* This is the generic routine we call when the Guest sends some DMA out. */
static void handle_output(int fd, unsigned long dma, unsigned long key,
struct device_list *devices)
{
......@@ -602,30 +918,53 @@ static void handle_output(int fd, unsigned long dma, unsigned long key,
struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
unsigned num = 0;
/* Convert the "struct lguest_dma" they're sending to a "struct
* iovec". */
lenp = dma2iov(dma, iov, &num);
/* Check each device: if they expect output to this key, tell them to
* handle it. */
for (i = devices->dev; i; i = i->next) {
if (i->handle_output && key == i->watch_key) {
/* We write the result straight into the used_len field
* for them. */
*lenp = i->handle_output(fd, iov, num, i);
return;
}
}
/* This can happen: the kernel sends any SEND_DMA which doesn't match
* another Guest to us. It could be that another Guest just left a
* network, for example. But it's unusual. */
warnx("Pending dma %p, key %p", (void *)dma, (void *)key);
}
/* This is called when the waker wakes us up: check for incoming file
* descriptors. */
static void handle_input(int fd, struct device_list *devices)
{
/* select() wants a zeroed timeval to mean "don't wait". */
struct timeval poll = { .tv_sec = 0, .tv_usec = 0 };
for (;;) {
struct device *i;
fd_set fds = devices->infds;
/* If nothing is ready, we're done. */
if (select(devices->max_infd+1, &fds, NULL, NULL, &poll) == 0)
break;
/* Otherwise, call the device(s) which have readable
* file descriptors and a method of handling them. */
for (i = devices->dev; i; i = i->next) {
if (i->handle_input && FD_ISSET(i->fd, &fds)) {
/* If handle_input() returns false, it means we
* should no longer service it.
* handle_console_input() does this. */
if (!i->handle_input(fd, i)) {
/* Clear it from the set of input file
* descriptors kept at the head of the
* device list. */
FD_CLR(i->fd, &devices->infds);
/* Tell waker to ignore it too... */
write(waker_fd, &i->fd, sizeof(i->fd));
......@@ -635,6 +974,15 @@ static void handle_input(int fd, struct device_list *devices)
}
}
/*L:190
* Device Setup
*
* All devices need a descriptor so the Guest knows it exists, and a "struct
* device" so the Launcher can keep track of it. We have common helper
* routines to allocate them.
*
* This routine allocates a new "struct lguest_device_desc" from descriptor
* table in the devices array just above the Guest's normal memory. */
static struct lguest_device_desc *
new_dev_desc(struct lguest_device_desc *descs,
u16 type, u16 features, u16 num_pages)
......@@ -646,6 +994,8 @@ new_dev_desc(struct lguest_device_desc *descs,
descs[i].type = type;
descs[i].features = features;
descs[i].num_pages = num_pages;
/* If they said the device needs memory, we allocate
* that now, bumping up the top of Guest memory. */
if (num_pages) {
map_zeroed_pages(top, num_pages);
descs[i].pfn = top/getpagesize();
......@@ -657,6 +1007,9 @@ new_dev_desc(struct lguest_device_desc *descs,
errx(1, "too many devices");
}
/* This monster routine does all the creation and setup of a new device,
* including caling new_dev_desc() to allocate the descriptor and device
* memory. */
static struct device *new_device(struct device_list *devices,
u16 type, u16 num_pages, u16 features,
int fd,
......@@ -669,12 +1022,18 @@ static struct device *new_device(struct device_list *devices,
{
struct device *dev = malloc(sizeof(*dev));
/* Append to device list. */
/* Append to device list. Prepending to a single-linked list is
* easier, but the user expects the devices to be arranged on the bus
* in command-line order. The first network device on the command line
* is eth0, the first block device /dev/lgba, etc. */
*devices->lastdev = dev;
dev->next = NULL;
devices->lastdev = &dev->next;
/* Now we populate the fields one at a time. */
dev->fd = fd;
/* If we have an input handler for this file descriptor, then we add it
* to the device_list's fdset and maxfd. */
if (handle_input)
set_fd(dev->fd, devices);
dev->desc = new_dev_desc(devices->descs, type, features, num_pages);
......@@ -685,27 +1044,37 @@ static struct device *new_device(struct device_list *devices,
return dev;
}
/* Our first setup routine is the console. It's a fairly simple device, but
* UNIX tty handling makes it uglier than it could be. */
static void setup_console(struct device_list *devices)
{
struct device *dev;
/* If we can save the initial standard input settings... */
if (tcgetattr(STDIN_FILENO, &orig_term) == 0) {
struct termios term = orig_term;
/* Then we turn off echo, line buffering and ^C etc. We want a
* raw input stream to the Guest. */
term.c_lflag &= ~(ISIG|ICANON|ECHO);
tcsetattr(STDIN_FILENO, TCSANOW, &term);
/* If we exit gracefully, the original settings will be
* restored so the user can see what they're typing. */
atexit(restore_term);
}
/* We don't currently require a page for the console. */
/* We don't currently require any memory for the console, so we ask for
* 0 pages. */
dev = new_device(devices, LGUEST_DEVICE_T_CONSOLE, 0, 0,
STDIN_FILENO, handle_console_input,
LGUEST_CONSOLE_DMA_KEY, handle_console_output);
/* We store the console state in dev->priv, and initialize it. */
dev->priv = malloc(sizeof(struct console_abort));
((struct console_abort *)dev->priv)->count = 0;
verbose("device %p: console\n",
(void *)(dev->desc->pfn * getpagesize()));
}
/* Setting up a block file is also fairly straightforward. */
static void setup_block_file(const char *filename, struct device_list *devices)
{
int fd;
......@@ -713,20 +1082,47 @@ static void setup_block_file(const char *filename, struct device_list *devices)
off64_t *device_len;
struct lguest_block_page *p;
/* We open with O_LARGEFILE because otherwise we get stuck at 2G. We
* open with O_DIRECT because otherwise our benchmarks go much too
* fast. */
fd = open_or_die(filename, O_RDWR|O_LARGEFILE|O_DIRECT);
/* We want one page, and have no input handler (the block file never
* has anything interesting to say to us). Our timing will be quite
* random, so it should be a reasonable randomness source. */
dev = new_device(devices, LGUEST_DEVICE_T_BLOCK, 1,
LGUEST_DEVICE_F_RANDOMNESS,
fd, NULL, 0, handle_block_output);
/* We store the device size in the private area */
device_len = dev->priv = malloc(sizeof(*device_len));
/* This is the safe way of establishing the size of our device: it
* might be a normal file or an actual block device like /dev/hdb. */
*device_len = lseek64(fd, 0, SEEK_END);
p = dev->mem;
/* The device memory is a "struct lguest_block_page". It's zeroed
* already, we just need to put in the device size. Block devices
* think in sectors (ie. 512 byte chunks), so we translate here. */
p = dev->mem;
p->num_sectors = *device_len/512;
verbose("device %p: block %i sectors\n",
(void *)(dev->desc->pfn * getpagesize()), p->num_sectors);
}
/* We use fnctl locks to reserve network slots (autocleanup!) */
/*
* Network Devices.
*
* Setting up network devices is quite a pain, because we have three types.
* First, we have the inter-Guest network. This is a file which is mapped into
* the address space of the Guests who are on the network. Because it is a
* shared mapping, the same page underlies all the devices, and they can send
* DMA to each other.
*
* Remember from our network driver, the Guest is told what slot in the page it
* is to use. We use exclusive fnctl locks to reserve a slot. If another
* Guest is using a slot, the lock will fail and we try another. Because fnctl
* locks are cleaned up automatically when we die, this cleverly means that our
* reservation on the slot will vanish if we crash. */
static unsigned int find_slot(int netfd, const char *filename)
{
struct flock fl;
......@@ -734,26 +1130,33 @@ static unsigned int find_slot(int netfd, const char *filename)
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_len = 1;
/* Try a 1 byte lock in each possible position number */
for (fl.l_start = 0;
fl.l_start < getpagesize()/sizeof(struct lguest_net);
fl.l_start++) {
/* If we succeed, return the slot number. */
if (fcntl(netfd, F_SETLK, &fl) == 0)
return fl.l_start;
}
errx(1, "No free slots in network file %s", filename);
}
/* This function sets up the network file */
static void setup_net_file(const char *filename,
struct device_list *devices)
{
int netfd;
struct device *dev;
/* We don't use open_or_die() here: for friendliness we create the file
* if it doesn't already exist. */
netfd = open(filename, O_RDWR, 0);
if (netfd < 0) {
if (errno == ENOENT) {
netfd = open(filename, O_RDWR|O_CREAT, 0600);
if (netfd >= 0) {
/* If we succeeded, initialize the file with a
* blank page. */
char page[getpagesize()];
memset(page, 0, sizeof(page));
write(netfd, page, sizeof(page));
......@@ -763,11 +1166,15 @@ static void setup_net_file(const char *filename,
err(1, "cannot open net file '%s'", filename);
}
/* We need 1 page, and the features indicate the slot to use and that
* no checksum is needed. We never touch this device again; it's
* between the Guests on the network, so we don't register input or
* output handlers. */
dev = new_device(devices, LGUEST_DEVICE_T_NET, 1,
find_slot(netfd, filename)|LGUEST_NET_F_NOCSUM,
-1, NULL, 0, NULL);
/* We overwrite the /dev/zero mapping with the actual file. */
/* Map the shared file. */
if (mmap(dev->mem, getpagesize(), PROT_READ|PROT_WRITE,
MAP_FIXED|MAP_SHARED, netfd, 0) != dev->mem)
err(1, "could not mmap '%s'", filename);
......@@ -775,6 +1182,7 @@ static void setup_net_file(const char *filename,
(void *)(dev->desc->pfn * getpagesize()), filename,
dev->desc->features & ~LGUEST_NET_F_NOCSUM);
}
/*:*/
static u32 str2ip(const char *ipaddr)
{
......@@ -784,7 +1192,11 @@ static u32 str2ip(const char *ipaddr)
return (byte[0] << 24) | (byte[1] << 16) | (byte[2] << 8) | byte[3];
}
/* adapted from libbridge */
/* This code is "adapted" from libbridge: it attaches the Host end of the
* network device to the bridge device specified by the command line.
*
* This is yet another James Morris contribution (I'm an IP-level guy, so I
* dislike bridging), and I just try not to break it. */
static void add_to_bridge(int fd, const char *if_name, const char *br_name)
{
int ifidx;
......@@ -803,12 +1215,16 @@ static void add_to_bridge(int fd, const char *if_name, const char *br_name)
err(1, "can't add %s to bridge %s", if_name, br_name);
}
/* This sets up the Host end of the network device with an IP address, brings
* it up so packets will flow, the copies the MAC address into the hwaddr
* pointer (in practice, the Host's slot in the network device's memory). */
static void configure_device(int fd, const char *devname, u32 ipaddr,
unsigned char hwaddr[6])
{
struct ifreq ifr;
struct sockaddr_in *sin = (struct sockaddr_in *)&ifr.ifr_addr;
/* Don't read these incantations. Just cut & paste them like I did! */
memset(&ifr, 0, sizeof(ifr));
strcpy(ifr.ifr_name, devname);
sin->sin_family = AF_INET;
......@@ -819,12 +1235,19 @@ static void configure_device(int fd, const char *devname, u32 ipaddr,
if (ioctl(fd, SIOCSIFFLAGS, &ifr) != 0)
err(1, "Bringing interface %s up", devname);
/* SIOC stands for Socket I/O Control. G means Get (vs S for Set
* above). IF means Interface, and HWADDR is hardware address.
* Simple! */
if (ioctl(fd, SIOCGIFHWADDR, &ifr) != 0)
err(1, "getting hw address for %s", devname);
memcpy(hwaddr, ifr.ifr_hwaddr.sa_data, 6);
}
/*L:195 The other kind of network is a Host<->Guest network. This can either
* use briding or routing, but the principle is the same: it uses the "tun"
* device to inject packets into the Host as if they came in from a normal
* network card. We just shunt packets between the Guest and the tun
* device. */
static void setup_tun_net(const char *arg, struct device_list *devices)
{
struct device *dev;
......@@ -833,36 +1256,56 @@ static void setup_tun_net(const char *arg, struct device_list *devices)
u32 ip;
const char *br_name = NULL;
/* We open the /dev/net/tun device and tell it we want a tap device. A
* tap device is like a tun device, only somehow different. To tell
* the truth, I completely blundered my way through this code, but it
* works now! */
netfd = open_or_die("/dev/net/tun", O_RDWR);
memset(&ifr, 0, sizeof(ifr));
ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
strcpy(ifr.ifr_name, "tap%d");
if (ioctl(netfd, TUNSETIFF, &ifr) != 0)
err(1, "configuring /dev/net/tun");
/* We don't need checksums calculated for packets coming in this
* device: trust us! */
ioctl(netfd, TUNSETNOCSUM, 1);
/* You will be peer 1: we should create enough jitter to randomize */
/* We create the net device with 1 page, using the features field of
* the descriptor to tell the Guest it is in slot 1 (NET_PEERNUM), and
* that the device has fairly random timing. We do *not* specify
* LGUEST_NET_F_NOCSUM: these packets can reach the real world.
*
* We will put our MAC address is slot 0 for the Guest to see, so
* it will send packets to us using the key "peer_offset(0)": */
dev = new_device(devices, LGUEST_DEVICE_T_NET, 1,
NET_PEERNUM|LGUEST_DEVICE_F_RANDOMNESS, netfd,
handle_tun_input, peer_offset(0), handle_tun_output);
/* We keep a flag which says whether we've seen packets come out from
* this network device. */
dev->priv = malloc(sizeof(bool));
*(bool *)dev->priv = false;
/* We need a socket to perform the magic network ioctls to bring up the
* tap interface, connect to the bridge etc. Any socket will do! */
ipfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
if (ipfd < 0)
err(1, "opening IP socket");
/* If the command line was --tunnet=bridge:<name> do bridging. */
if (!strncmp(BRIDGE_PFX, arg, strlen(BRIDGE_PFX))) {
ip = INADDR_ANY;
br_name = arg + strlen(BRIDGE_PFX);
add_to_bridge(ipfd, ifr.ifr_name, br_name);
} else
} else /* It is an IP address to set up the device with */
ip = str2ip(arg);
/* We are peer 0, ie. first slot. */
/* We are peer 0, ie. first slot, so we hand dev->mem to this routine
* to write the MAC address at the start of the device memory. */
configure_device(ipfd, ifr.ifr_name, ip, dev->mem);
/* Set "promisc" bit: we want every single packet. */
/* Set "promisc" bit: we want every single packet if we're going to
* bridge to other machines (and otherwise it doesn't matter). */
*((u8 *)dev->mem) |= 0x1;
close(ipfd);
......@@ -873,7 +1316,10 @@ static void setup_tun_net(const char *arg, struct device_list *devices)
if (br_name)
verbose("attached to bridge: %s\n", br_name);
}
/* That's the end of device setup. */
/*L:220 Finally we reach the core of the Launcher, which runs the Guest, serves
* its input and output, and finally, lays it to rest. */
static void __attribute__((noreturn))
run_guest(int lguest_fd, struct device_list *device_list)
{
......@@ -885,20 +1331,37 @@ run_guest(int lguest_fd, struct device_list *device_list)
/* We read from the /dev/lguest device to run the Guest. */
readval = read(lguest_fd, arr, sizeof(arr));
/* The read can only really return sizeof(arr) (the Guest did a
* SEND_DMA to us), or an error. */
/* For a successful read, arr[0] is the address of the "struct
* lguest_dma", and arr[1] is the key the Guest sent to. */
if (readval == sizeof(arr)) {
handle_output(lguest_fd, arr[0], arr[1], device_list);
continue;
/* ENOENT means the Guest died. Reading tells us why. */
} else if (errno == ENOENT) {
char reason[1024] = { 0 };
read(lguest_fd, reason, sizeof(reason)-1);
errx(1, "%s", reason);
/* EAGAIN means the waker wanted us to look at some input.
* Anything else means a bug or incompatible change. */
} else if (errno != EAGAIN)
err(1, "Running guest failed");
/* Service input, then unset the BREAK which releases
* the Waker. */
handle_input(lguest_fd, device_list);
if (write(lguest_fd, args, sizeof(args)) < 0)
err(1, "Resetting break");
}
}
/*
* This is the end of the Launcher.
*
* But wait! We've seen I/O from the Launcher, and we've seen I/O from the
* Drivers. If we were to see the Host kernel I/O code, our understanding
* would be complete... :*/
static struct option opts[] = {
{ "verbose", 0, NULL, 'v' },
......@@ -916,20 +1379,49 @@ static void usage(void)
"<mem-in-mb> vmlinux [args...]");
}
/*L:100 The Launcher code itself takes us out into userspace, that scary place
* where pointers run wild and free! Unfortunately, like most userspace
* programs, it's quite boring (which is why everyone like to hack on the
* kernel!). Perhaps if you make up an Lguest Drinking Game at this point, it
* will get you through this section. Or, maybe not.
*
* The Launcher binary sits up high, usually starting at address 0xB8000000.
* Everything below this is the "physical" memory for the Guest. For example,
* if the Guest were to write a "1" at physical address 0, we would see a "1"
* in the Launcher at "(int *)0". Guest physical == Launcher virtual.
*
* This can be tough to get your head around, but usually it just means that we
* don't need to do any conversion when the Guest gives us it's "physical"
* addresses.
*/
int main(int argc, char *argv[])
{
/* Memory, top-level pagetable, code startpoint, PAGE_OFFSET and size
* of the (optional) initrd. */
unsigned long mem = 0, pgdir, start, page_offset, initrd_size = 0;
/* A temporary and the /dev/lguest file descriptor. */
int i, c, lguest_fd;
/* The list of Guest devices, based on command line arguments. */
struct device_list device_list;
/* The boot information for the Guest: at guest-physical address 0. */
void *boot = (void *)0;
/* If they specify an initrd file to load. */
const char *initrd_name = NULL;
/* First we initialize the device list. Since console and network
* device receive input from a file descriptor, we keep an fdset
* (infds) and the maximum fd number (max_infd) with the head of the
* list. We also keep a pointer to the last device, for easy appending
* to the list. */
device_list.max_infd = -1;
device_list.dev = NULL;
device_list.lastdev = &device_list.dev;
FD_ZERO(&device_list.infds);
/* We need to know how much memory so we can allocate devices. */
/* We need to know how much memory so we can set up the device
* descriptor and memory pages for the devices as we parse the command
* line. So we quickly look through the arguments to find the amount
* of memory now. */
for (i = 1; i < argc; i++) {
if (argv[i][0] != '-') {
mem = top = atoi(argv[i]) * 1024 * 1024;
......@@ -938,6 +1430,8 @@ int main(int argc, char *argv[])
break;
}
}
/* The options are fairly straight-forward */
while ((c = getopt_long(argc, argv, "v", opts, NULL)) != EOF) {
switch (c) {
case 'v':
......@@ -960,42 +1454,59 @@ int main(int argc, char *argv[])
usage();
}
}
/* After the other arguments we expect memory and kernel image name,
* followed by command line arguments for the kernel. */
if (optind + 2 > argc)
usage();
/* We need a console device */
/* We always have a console device */
setup_console(&device_list);
/* First we map /dev/zero over all of guest-physical memory. */
/* We start by mapping anonymous pages over all of guest-physical
* memory range. This fills it with 0, and ensures that the Guest
* won't be killed when it tries to access it. */
map_zeroed_pages(0, mem / getpagesize());
/* Now we load the kernel */
start = load_kernel(open_or_die(argv[optind+1], O_RDONLY),
&page_offset);
/* Map the initrd image if requested */
/* Map the initrd image if requested (at top of physical memory) */
if (initrd_name) {
initrd_size = load_initrd(initrd_name, mem);
/* These are the location in the Linux boot header where the
* start and size of the initrd are expected to be found. */
*(unsigned long *)(boot+0x218) = mem - initrd_size;
*(unsigned long *)(boot+0x21c) = initrd_size;
/* The bootloader type 0xFF means "unknown"; that's OK. */
*(unsigned char *)(boot+0x210) = 0xFF;
}
/* Set up the initial linar pagetables. */
/* Set up the initial linear pagetables, starting below the initrd. */
pgdir = setup_pagetables(mem, initrd_size, page_offset);
/* E820 memory map: ours is a simple, single region. */
/* The Linux boot header contains an "E820" memory map: ours is a
* simple, single region. */
*(char*)(boot+E820NR) = 1;
*((struct e820entry *)(boot+E820MAP))
= ((struct e820entry) { 0, mem, E820_RAM });
/* Command line pointer and command line (at 4096) */
/* The boot header contains a command line pointer: we put the command
* line after the boot header (at address 4096) */
*(void **)(boot + 0x228) = boot + 4096;
concat(boot + 4096, argv+optind+2);
/* Paravirt type: 1 == lguest */
/* The guest type value of "1" tells the Guest it's under lguest. */
*(int *)(boot + 0x23c) = 1;
/* We tell the kernel to initialize the Guest: this returns the open
* /dev/lguest file descriptor. */
lguest_fd = tell_kernel(pgdir, start, page_offset);
/* We fork off a child process, which wakes the Launcher whenever one
* of the input file descriptors needs attention. Otherwise we would
* run the Guest until it tries to output something. */
waker_fd = setup_waker(lguest_fd, &device_list);
/* Finally, run the Guest. This doesn't return. */
run_guest(lguest_fd, &device_list);
}
drivers/lguest/core.c
View file @ dde79789
......@@ -208,24 +208,39 @@ static int emulate_insn(struct lguest *lg)
return 1;
}
/*L:305
* Dealing With Guest Memory.
*
* When the Guest gives us (what it thinks is) a physical address, we can use
* the normal copy_from_user() & copy_to_user() on that address: remember,
* Guest physical == Launcher virtual.
*
* But we can't trust the Guest: it might be trying to access the Launcher
* code. We have to check that the range is below the pfn_limit the Launcher
* gave us. We have to make sure that addr + len doesn't give us a false
* positive by overflowing, too. */
int lguest_address_ok(const struct lguest *lg,
unsigned long addr, unsigned long len)
{
return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
}
/* Just like get_user, but don't let guest access lguest binary. */
/* This is a convenient routine to get a 32-bit value from the Guest (a very
* common operation). Here we can see how useful the kill_lguest() routine we
* met in the Launcher can be: we return a random value (0) instead of needing
* to return an error. */
u32 lgread_u32(struct lguest *lg, unsigned long addr)
{
u32 val = 0;
/* Don't let them access lguest binary */
/* Don't let them access lguest binary. */
if (!lguest_address_ok(lg, addr, sizeof(val))
|| get_user(val, (u32 __user *)addr) != 0)
kill_guest(lg, "bad read address %#lx", addr);
return val;
}
/* Same thing for writing a value. */
void lgwrite_u32(struct lguest *lg, unsigned long addr, u32 val)
{
if (!lguest_address_ok(lg, addr, sizeof(val))
......@@ -233,6 +248,9 @@ void lgwrite_u32(struct lguest *lg, unsigned long addr, u32 val)
kill_guest(lg, "bad write address %#lx", addr);
}
/* This routine is more generic, and copies a range of Guest bytes into a
* buffer. If the copy_from_user() fails, we fill the buffer with zeroes, so
* the caller doesn't end up using uninitialized kernel memory. */
void lgread(struct lguest *lg, void *b, unsigned long addr, unsigned bytes)
{
if (!lguest_address_ok(lg, addr, bytes)
......@@ -243,6 +261,7 @@ void lgread(struct lguest *lg, void *b, unsigned long addr, unsigned bytes)
}
}
/* Similarly, our generic routine to copy into a range of Guest bytes. */
void lgwrite(struct lguest *lg, unsigned long addr, const void *b,
unsigned bytes)
{
......@@ -250,6 +269,7 @@ void lgwrite(struct lguest *lg, unsigned long addr, const void *b,
|| copy_to_user((void __user *)addr, b, bytes) != 0)
kill_guest(lg, "bad write address %#lx len %u", addr, bytes);
}
/* (end of memory access helper routines) :*/
static void set_ts(void)
{
......
drivers/lguest/io.c
View file @ dde79789
......@@ -27,8 +27,36 @@
#include <linux/uaccess.h>
#include "lg.h"
/*L:300
* I/O
*
* Getting data in and out of the Guest is quite an art. There are numerous
* ways to do it, and they all suck differently. We try to keep things fairly
* close to "real" hardware so our Guest's drivers don't look like an alien
* visitation in the middle of the Linux code, and yet make sure that Guests
* can talk directly to other Guests, not just the Launcher.
*
* To do this, the Guest gives us a key when it binds or sends DMA buffers.
* The key corresponds to a "physical" address inside the Guest (ie. a virtual
* address inside the Launcher process). We don't, however, use this key
* directly.
*
* We want Guests which share memory to be able to DMA to each other: two
* Launchers can mmap memory the same file, then the Guests can communicate.
* Fortunately, the futex code provides us with a way to get a "union
* futex_key" corresponding to the memory lying at a virtual address: if the
* two processes share memory, the "union futex_key" for that memory will match
* even if the memory is mapped at different addresses in each. So we always
* convert the keys to "union futex_key"s to compare them.
*
* Before we dive into this though, we need to look at another set of helper
* routines used throughout the Host kernel code to access Guest memory.
:*/
static struct list_head dma_hash[61];
/* An unfortunate side effect of the Linux double-linked list implementation is
* that there's no good way to statically initialize an array of linked
* lists. */
void lguest_io_init(void)
{
unsigned int i;
......@@ -60,6 +88,19 @@ static int check_dma_list(struct lguest *lg, const struct lguest_dma *dma)
return 0;
}
/*L:330 This is our hash function, using the wonderful Jenkins hash.
*
* The futex key is a union with three parts: an unsigned long word, a pointer,
* and an int "offset". We could use jhash_2words() which takes three u32s.
* (Ok, the hash functions are great: the naming sucks though).
*
* It's nice to be portable to 64-bit platforms, so we use the more generic
* jhash2(), which takes an array of u32, the number of u32s, and an initial
* u32 to roll in. This is uglier, but breaks down to almost the same code on
* 32-bit platforms like this one.
*
* We want a position in the array, so we modulo ARRAY_SIZE(dma_hash) (ie. 61).
*/
static unsigned int hash(const union futex_key *key)
{
return jhash2((u32*)&key->both.word,
......@@ -68,6 +109,9 @@ static unsigned int hash(const union futex_key *key)
% ARRAY_SIZE(dma_hash);
}
/* This is a convenience routine to compare two keys. It's a much bemoaned C
* weakness that it doesn't allow '==' on structures or unions, so we have to
* open-code it like this. */
static inline int key_eq(const union futex_key *a, const union futex_key *b)
{
return (a->both.word == b->both.word
......@@ -75,22 +119,36 @@ static inline int key_eq(const union futex_key *a, const union futex_key *b)
&& a->both.offset == b->both.offset);
}
/* Must hold read lock on dmainfo owner's current->mm->mmap_sem */
/*L:360 OK, when we need to actually free up a Guest's DMA array we do several
* things, so we have a convenient function to do it.
*
* The caller must hold a read lock on dmainfo owner's current->mm->mmap_sem
* for the drop_futex_key_refs(). */
static void unlink_dma(struct lguest_dma_info *dmainfo)
{
/* You locked this too, right? */
BUG_ON(!mutex_is_locked(&lguest_lock));
/* This is how we know that the entry is free. */
dmainfo->interrupt = 0;
/* Remove it from the hash table. */
list_del(&dmainfo->list);
/* Drop the references we were holding (to the inode or mm). */
drop_futex_key_refs(&dmainfo->key);
}
/*L:350 This is the routine which we call when the Guest asks to unregister a
* DMA array attached to a given key. Returns true if the array was found. */
static int unbind_dma(struct lguest *lg,
const union futex_key *key,
unsigned long dmas)
{
int i, ret = 0;
/* We don't bother with the hash table, just look through all this
* Guest's DMA arrays. */
for (i = 0; i < LGUEST_MAX_DMA; i++) {
/* In theory it could have more than one array on the same key,
* or one array on multiple keys, so we check both */
if (key_eq(key, &lg->dma[i].key) && dmas == lg->dma[i].dmas) {
unlink_dma(&lg->dma[i]);
ret = 1;
......@@ -100,51 +158,91 @@ static int unbind_dma(struct lguest *lg,
return ret;
}
/*L:340 BIND_DMA: this is the hypercall which sets up an array of "struct
* lguest_dma" for receiving I/O.
*
* The Guest wants to bind an array of "struct lguest_dma"s to a particular key
* to receive input. This only happens when the Guest is setting up a new
* device, so it doesn't have to be very fast.
*
* It returns 1 on a successful registration (it can fail if we hit the limit
* of registrations for this Guest).
*/
int bind_dma(struct lguest *lg,
unsigned long ukey, unsigned long dmas, u16 numdmas, u8 interrupt)
{
unsigned int i;
int ret = 0;
union futex_key key;
/* Futex code needs the mmap_sem. */
struct rw_semaphore *fshared = &current->mm->mmap_sem;
/* Invalid interrupt? (We could kill the guest here). */
if (interrupt >= LGUEST_IRQS)
return 0;
/* We need to grab the Big Lguest Lock, because other Guests may be
* trying to look through this Guest's DMAs to send something while
* we're doing this. */
mutex_lock(&lguest_lock);
down_read(fshared);
if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
kill_guest(lg, "bad dma key %#lx", ukey);
goto unlock;
}
/* We want to keep this key valid once we drop mmap_sem, so we have to
* hold a reference. */
get_futex_key_refs(&key);
/* If the Guest specified an interrupt of 0, that means they want to
* unregister this array of "struct lguest_dma"s. */
if (interrupt == 0)
ret = unbind_dma(lg, &key, dmas);
else {
/* Look through this Guest's dma array for an unused entry. */
for (i = 0; i < LGUEST_MAX_DMA; i++) {
/* If the interrupt is non-zero, the entry is already
* used. */
if (lg->dma[i].interrupt)
continue;
/* OK, a free one! Fill on our details. */
lg->dma[i].dmas = dmas;
lg->dma[i].num_dmas = numdmas;
lg->dma[i].next_dma = 0;
lg->dma[i].key = key;
lg->dma[i].guestid = lg->guestid;
lg->dma[i].interrupt = interrupt;
/* Now we add it to the hash table: the position
* depends on the futex key that we got. */
list_add(&lg->dma[i].list, &dma_hash[hash(&key)]);
/* Success! */
ret = 1;
goto unlock;
}
}
/* If we didn't find a slot to put the key in, drop the reference
* again. */
drop_futex_key_refs(&key);
unlock:
/* Unlock and out. */
up_read(fshared);
mutex_unlock(&lguest_lock);
return ret;
}
/* lgread from another guest */
/*L:385 Note that our routines to access a different Guest's memory are called
* lgread_other() and lgwrite_other(): these names emphasize that they are only
* used when the Guest is *not* the current Guest.
*
* The interface for copying from another process's memory is called
* access_process_vm(), with a final argument of 0 for a read, and 1 for a
* write.
*
* We need lgread_other() to read the destination Guest's "struct lguest_dma"
* array. */
static int lgread_other(struct lguest *lg,
void *buf, u32 addr, unsigned bytes)
{
......@@ -157,7 +255,8 @@ static int lgread_other(struct lguest *lg,
return 1;
}
/* lgwrite to another guest */
/* "lgwrite()" to another Guest: used to update the destination "used_len" once
* we've transferred data into the buffer. */
static int lgwrite_other(struct lguest *lg, u32 addr,
const void *buf, unsigned bytes)
{
......@@ -170,6 +269,15 @@ static int lgwrite_other(struct lguest *lg, u32 addr,
return 1;
}
/*L:400 This is the generic engine which copies from a source "struct
* lguest_dma" from this Guest into another Guest's "struct lguest_dma". The
* destination Guest's pages have already been mapped, as contained in the
* pages array.
*
* If you're wondering if there's a nice "copy from one process to another"
* routine, so was I. But Linux isn't really set up to copy between two
* unrelated processes, so we have to write it ourselves.
*/
static u32 copy_data(struct lguest *srclg,
const struct lguest_dma *src,
const struct lguest_dma *dst,
......@@ -178,33 +286,59 @@ static u32 copy_data(struct lguest *srclg,
unsigned int totlen, si, di, srcoff, dstoff;
void *maddr = NULL;
/* We return the total length transferred. */
totlen = 0;
/* We keep indexes into the source and destination "struct lguest_dma",
* and an offset within each region. */
si = di = 0;
srcoff = dstoff = 0;
/* We loop until the source or destination is exhausted. */
while (si < LGUEST_MAX_DMA_SECTIONS && src->len[si]
&& di < LGUEST_MAX_DMA_SECTIONS && dst->len[di]) {
/* We can only transfer the rest of the src buffer, or as much
* as will fit into the destination buffer. */
u32 len = min(src->len[si] - srcoff, dst->len[di] - dstoff);
/* For systems using "highmem" we need to use kmap() to access
* the page we want. We often use the same page over and over,
* so rather than kmap() it on every loop, we set the maddr
* pointer to NULL when we need to move to the next
* destination page. */
if (!maddr)
maddr = kmap(pages[di]);
/* FIXME: This is not completely portable, since
archs do different things for copy_to_user_page. */
/* Copy directly from (this Guest's) source address to the
* destination Guest's kmap()ed buffer. Note that maddr points
* to the start of the page: we need to add the offset of the
* destination address and offset within the buffer. */
/* FIXME: This is not completely portable. I looked at
* copy_to_user_page(), and some arch's seem to need special
* flushes. x86 is fine. */
if (copy_from_user(maddr + (dst->addr[di] + dstoff)%PAGE_SIZE,
(void __user *)src->addr[si], len) != 0) {
/* If a copy failed, it's the source's fault. */
kill_guest(srclg, "bad address in sending DMA");
totlen = 0;
break;
}
/* Increment the total and src & dst offsets */
totlen += len;
srcoff += len;
dstoff += len;
/* Presumably we reached the end of the src or dest buffers: */
if (srcoff == src->len[si]) {
/* Move to the next buffer at offset 0 */
si++;
srcoff = 0;
}
if (dstoff == dst->len[di]) {
/* We need to unmap that destination page and reset
* maddr ready for the next one. */
kunmap(pages[di]);
maddr = NULL;
di++;
......@@ -212,13 +346,15 @@ static u32 copy_data(struct lguest *srclg,
}
}
/* If we still had a page mapped at the end, unmap now. */
if (maddr)
kunmap(pages[di]);
return totlen;
}
/* Src is us, ie. current. */
/*L:390 This is how we transfer a "struct lguest_dma" from the source Guest
* (the current Guest which called SEND_DMA) to another Guest. */
static u32 do_dma(struct lguest *srclg, const struct lguest_dma *src,
struct lguest *dstlg, const struct lguest_dma *dst)
{
......@@ -226,23 +362,31 @@ static u32 do_dma(struct lguest *srclg, const struct lguest_dma *src,
u32 ret;
struct page *pages[LGUEST_MAX_DMA_SECTIONS];
/* We check that both source and destination "struct lguest_dma"s are
* within the bounds of the source and destination Guests */
if (!check_dma_list(dstlg, dst) || !check_dma_list(srclg, src))
return 0;
/* First get the destination pages */
/* We need to map the pages which correspond to each parts of
* destination buffer. */
for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
if (dst->len[i] == 0)
break;
/* get_user_pages() is a complicated function, especially since
* we only want a single page. But it works, and returns the
* number of pages. Note that we're holding the destination's
* mmap_sem, as get_user_pages() requires. */
if (get_user_pages(dstlg->tsk, dstlg->mm,
dst->addr[i], 1, 1, 1, pages+i, NULL)
!= 1) {
/* This means the destination gave us a bogus buffer */
kill_guest(dstlg, "Error mapping DMA pages");
ret = 0;
goto drop_pages;
}
}
/* Now copy until we run out of src or dst. */
/* Now copy the data until we run out of src or dst. */
ret = copy_data(srclg, src, dst, pages);
drop_pages:
......@@ -251,6 +395,11 @@ static u32 do_dma(struct lguest *srclg, const struct lguest_dma *src,
return ret;
}
/*L:380 Transferring data from one Guest to another is not as simple as I'd
* like. We've found the "struct lguest_dma_info" bound to the same address as
* the send, we need to copy into it.
*
* This function returns true if the destination array was empty. */
static int dma_transfer(struct lguest *srclg,
unsigned long udma,
struct lguest_dma_info *dst)
......@@ -259,15 +408,23 @@ static int dma_transfer(struct lguest *srclg,
struct lguest *dstlg;
u32 i, dma = 0;
/* From the "struct lguest_dma_info" we found in the hash, grab the
* Guest. */
dstlg = &lguests[dst->guestid];
/* Get our dma list. */
/* Read in the source "struct lguest_dma" handed to SEND_DMA. */
lgread(srclg, &src_dma, udma, sizeof(src_dma));
/* We can't deadlock against them dmaing to us, because this
* is all under the lguest_lock. */
/* We need the destination's mmap_sem, and we already hold the source's
* mmap_sem for the futex key lookup. Normally this would suggest that
* we could deadlock if the destination Guest was trying to send to
* this source Guest at the same time, which is another reason that all
* I/O is done under the big lguest_lock. */
down_read(&dstlg->mm->mmap_sem);
/* Look through the destination DMA array for an available buffer. */
for (i = 0; i < dst->num_dmas; i++) {
/* We keep a "next_dma" pointer which often helps us avoid
* looking at lots of previously-filled entries. */
dma = (dst->next_dma + i) % dst->num_dmas;
if (!lgread_other(dstlg, &dst_dma,
dst->dmas + dma * sizeof(struct lguest_dma),
......@@ -277,30 +434,46 @@ static int dma_transfer(struct lguest *srclg,
if (!dst_dma.used_len)
break;
}
/* If we found a buffer, we do the actual data copy. */
if (i != dst->num_dmas) {
unsigned long used_lenp;
unsigned int ret;
ret = do_dma(srclg, &src_dma, dstlg, &dst_dma);
/* Put used length in src. */
/* Put used length in the source "struct lguest_dma"'s used_len
* field. It's a little tricky to figure out where that is,
* though. */
lgwrite_u32(srclg,
udma+offsetof(struct lguest_dma, used_len), ret);
/* Tranferring 0 bytes is OK if the source buffer was empty. */
if (ret == 0 && src_dma.len[0] != 0)
goto fail;
/* Make sure destination sees contents before length. */
/* The destination Guest might be running on a different CPU:
* we have to make sure that it will see the "used_len" field
* change to non-zero *after* it sees the data we copied into
* the buffer. Hence a write memory barrier. */
wmb();
/* Figuring out where the destination's used_len field for this
* "struct lguest_dma" in the array is also a little ugly. */
used_lenp = dst->dmas
+ dma * sizeof(struct lguest_dma)
+ offsetof(struct lguest_dma, used_len);
lgwrite_other(dstlg, used_lenp, &ret, sizeof(ret));
/* Move the cursor for next time. */
dst->next_dma++;
}
up_read(&dstlg->mm->mmap_sem);
/* Do this last so dst doesn't simply sleep on lock. */
/* We trigger the destination interrupt, even if the destination was
* empty and we didn't transfer anything: this gives them a chance to
* wake up and refill. */
set_bit(dst->interrupt, dstlg->irqs_pending);
/* Wake up the destination process. */
wake_up_process(dstlg->tsk);
/* If we passed the last "struct lguest_dma", the receive had no
* buffers left. */
return i == dst->num_dmas;
fail:
......@@ -308,6 +481,8 @@ static int dma_transfer(struct lguest *srclg,
return 0;
}
/*L:370 This is the counter-side to the BIND_DMA hypercall; the SEND_DMA
* hypercall. We find out who's listening, and send to them. */
void send_dma(struct lguest *lg, unsigned long ukey, unsigned long udma)
{
union futex_key key;
......@@ -317,31 +492,43 @@ void send_dma(struct lguest *lg, unsigned long ukey, unsigned long udma)
again:
mutex_lock(&lguest_lock);
down_read(fshared);
/* Get the futex key for the key the Guest gave us */
if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
kill_guest(lg, "bad sending DMA key");
goto unlock;
}
/* Shared mapping? Look for other guests... */
/* Since the key must be a multiple of 4, the futex key uses the lower
* bit of the "offset" field (which would always be 0) to indicate a
* mapping which is shared with other processes (ie. Guests). */
if (key.shared.offset & 1) {
struct lguest_dma_info *i;
/* Look through the hash for other Guests. */
list_for_each_entry(i, &dma_hash[hash(&key)], list) {
/* Don't send to ourselves. */
if (i->guestid == lg->guestid)
continue;
if (!key_eq(&key, &i->key))
continue;
/* If dma_transfer() tells us the destination has no
* available buffers, we increment "empty". */
empty += dma_transfer(lg, udma, i);
break;
}
/* If the destination is empty, we release our locks and
* give the destination Guest a brief chance to restock. */
if (empty == 1) {
/* Give any recipients one chance to restock. */
up_read(&current->mm->mmap_sem);
mutex_unlock(&lguest_lock);
/* Next time, we won't try again. */
empty++;
goto again;
}
} else {
/* Private mapping: tell our userspace. */
/* Private mapping: Guest is sending to its Launcher. We set
* the "dma_is_pending" flag so that the main loop will exit
* and the Launcher's read() from /dev/lguest will return. */
lg->dma_is_pending = 1;
lg->pending_dma = udma;
lg->pending_key = ukey;
......@@ -350,6 +537,7 @@ void send_dma(struct lguest *lg, unsigned long ukey, unsigned long udma)
up_read(fshared);
mutex_unlock(&lguest_lock);
}
/*:*/
void release_all_dma(struct lguest *lg)
{
......@@ -365,7 +553,8 @@ void release_all_dma(struct lguest *lg)
up_read(&lg->mm->mmap_sem);
}
/* Userspace wants a dma buffer from this guest. */
/*L:320 This routine looks for a DMA buffer registered by the Guest on the
* given key (using the BIND_DMA hypercall). */
unsigned long get_dma_buffer(struct lguest *lg,
unsigned long ukey, unsigned long *interrupt)
{
......@@ -374,15 +563,29 @@ unsigned long get_dma_buffer(struct lguest *lg,
struct lguest_dma_info *i;
struct rw_semaphore *fshared = &current->mm->mmap_sem;
/* Take the Big Lguest Lock to stop other Guests sending this Guest DMA
* at the same time. */
mutex_lock(&lguest_lock);
/* To match between Guests sharing the same underlying memory we steal
* code from the futex infrastructure. This requires that we hold the
* "mmap_sem" for our process (the Launcher), and pass it to the futex
* code. */
down_read(fshared);
/* This can fail if it's not a valid address, or if the address is not
* divisible by 4 (the futex code needs that, we don't really). */
if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
kill_guest(lg, "bad registered DMA buffer");
goto unlock;
}
/* Search the hash table for matching entries (the Launcher can only
* send to its own Guest for the moment, so the entry must be for this
* Guest) */
list_for_each_entry(i, &dma_hash[hash(&key)], list) {
if (key_eq(&key, &i->key) && i->guestid == lg->guestid) {
unsigned int j;
/* Look through the registered DMA array for an
* available buffer. */
for (j = 0; j < i->num_dmas; j++) {
struct lguest_dma dma;
......@@ -391,6 +594,8 @@ unsigned long get_dma_buffer(struct lguest *lg,
if (dma.used_len == 0)
break;
}
/* Store the interrupt the Guest wants when the buffer
* is used. */
*interrupt = i->interrupt;
break;
}
......@@ -400,4 +605,12 @@ unsigned long get_dma_buffer(struct lguest *lg,
mutex_unlock(&lguest_lock);
return ret;
}
/*:*/
/*L:410 This really has completed the Launcher. Not only have we now finished
* the longest chapter in our journey, but this also means we are over halfway
* through!
*
* Enough prevaricating around the bush: it is time for us to dive into the
* core of the Host, in "make Host".
*/
drivers/lguest/lg.h
View file @ dde79789
......@@ -244,6 +244,30 @@ unsigned long get_dma_buffer(struct lguest *lg, unsigned long key,
/* hypercalls.c: */
void do_hypercalls(struct lguest *lg);
/*L:035
* Let's step aside for the moment, to study one important routine that's used
* widely in the Host code.
*
* There are many cases where the Guest does something invalid, like pass crap
* to a hypercall. Since only the Guest kernel can make hypercalls, it's quite
* acceptable to simply terminate the Guest and give the Launcher a nicely
* formatted reason. It's also simpler for the Guest itself, which doesn't
* need to check most hypercalls for "success"; if you're still running, it
* succeeded.
*
* Once this is called, the Guest will never run again, so most Host code can
* call this then continue as if nothing had happened. This means many
* functions don't have to explicitly return an error code, which keeps the
* code simple.
*
* It also means that this can be called more than once: only the first one is
* remembered. The only trick is that we still need to kill the Guest even if
* we can't allocate memory to store the reason. Linux has a neat way of
* packing error codes into invalid pointers, so we use that here.
*
* Like any macro which uses an "if", it is safely wrapped in a run-once "do {
* } while(0)".
*/
#define kill_guest(lg, fmt...) \
do { \
if (!(lg)->dead) { \
......@@ -252,6 +276,7 @@ do { \
(lg)->dead = ERR_PTR(-ENOMEM); \
} \
} while(0)
/* (End of aside) :*/
static inline unsigned long guest_pa(struct lguest *lg, unsigned long vaddr)
{
......
drivers/lguest/lguest_user.c
View file @ dde79789
......@@ -9,33 +9,62 @@
#include <linux/fs.h>
#include "lg.h"
/*L:030 setup_regs() doesn't really belong in this file, but it gives us an
* early glimpse deeper into the Host so it's worth having here.
*
* Most of the Guest's registers are left alone: we used get_zeroed_page() to
* allocate the structure, so they will be 0. */
static void setup_regs(struct lguest_regs *regs, unsigned long start)
{
/* Write out stack in format lguest expects, so we can switch to it. */
/* There are four "segment" registers which the Guest needs to boot:
* The "code segment" register (cs) refers to the kernel code segment
* __KERNEL_CS, and the "data", "extra" and "stack" segment registers
* refer to the kernel data segment __KERNEL_DS.
*
* The privilege level is packed into the lower bits. The Guest runs
* at privilege level 1 (GUEST_PL).*/
regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
regs->cs = __KERNEL_CS|GUEST_PL;
regs->eflags = 0x202; /* Interrupts enabled. */
/* The "eflags" register contains miscellaneous flags. Bit 1 (0x002)
* is supposed to always be "1". Bit 9 (0x200) controls whether
* interrupts are enabled. We always leave interrupts enabled while
* running the Guest. */
regs->eflags = 0x202;
/* The "Extended Instruction Pointer" register says where the Guest is
* running. */
regs->eip = start;
/* esi points to our boot information (physical address 0) */
/* %esi points to our boot information, at physical address 0, so don't
* touch it. */
}
/* + addr */
/*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a
* DMA buffer. This is done by writing LHREQ_GETDMA and the key to
* /dev/lguest. */
static long user_get_dma(struct lguest *lg, const u32 __user *input)
{
unsigned long key, udma, irq;
/* Fetch the key they wrote to us. */
if (get_user(key, input) != 0)
return -EFAULT;
/* Look for a free Guest DMA buffer bound to that key. */
udma = get_dma_buffer(lg, key, &irq);
if (!udma)
return -ENOENT;
/* We put irq number in udma->used_len. */
/* We need to tell the Launcher what interrupt the Guest expects after
* the buffer is filled. We stash it in udma->used_len. */
lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq);
/* The (guest-physical) address of the DMA buffer is returned from
* the write(). */
return udma;
}
/* To force the Guest to stop running and return to the Launcher, the
/*L:315 To force the Guest to stop running and return to the Launcher, the
* Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest. The
* Launcher then writes LHREQ_BREAK and "0" to release the Waker. */
static int break_guest_out(struct lguest *lg, const u32 __user *input)
......@@ -59,7 +88,8 @@ static int break_guest_out(struct lguest *lg, const u32 __user *input)
}
}
/* + irq */
/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
* number to /dev/lguest. */
static int user_send_irq(struct lguest *lg, const u32 __user *input)
{
u32 irq;
......@@ -68,14 +98,19 @@ static int user_send_irq(struct lguest *lg, const u32 __user *input)
return -EFAULT;
if (irq >= LGUEST_IRQS)
return -EINVAL;
/* Next time the Guest runs, the core code will see if it can deliver
* this interrupt. */
set_bit(irq, lg->irqs_pending);
return 0;
}
/*L:040 Once our Guest is initialized, the Launcher makes it run by reading
* from /dev/lguest. */
static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
{
struct lguest *lg = file->private_data;
/* You must write LHREQ_INITIALIZE first! */
if (!lg)
return -EINVAL;
......@@ -83,27 +118,52 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
if (current != lg->tsk)
return -EPERM;
/* If the guest is already dead, we indicate why */
if (lg->dead) {
size_t len;
/* lg->dead either contains an error code, or a string. */
if (IS_ERR(lg->dead))
return PTR_ERR(lg->dead);
/* We can only return as much as the buffer they read with. */
len = min(size, strlen(lg->dead)+1);
if (copy_to_user(user, lg->dead, len) != 0)
return -EFAULT;
return len;
}
/* If we returned from read() last time because the Guest sent DMA,
* clear the flag. */
if (lg->dma_is_pending)
lg->dma_is_pending = 0;
/* Run the Guest until something interesting happens. */
return run_guest(lg, (unsigned long __user *)user);
}
/* Take: pfnlimit, pgdir, start, pageoffset. */
/*L:020 The initialization write supplies 4 32-bit values (in addition to the
* 32-bit LHREQ_INITIALIZE value). These are:
*
* pfnlimit: The highest (Guest-physical) page number the Guest should be
* allowed to access. The Launcher has to live in Guest memory, so it sets
* this to ensure the Guest can't reach it.
*
* pgdir: The (Guest-physical) address of the top of the initial Guest
* pagetables (which are set up by the Launcher).
*
* start: The first instruction to execute ("eip" in x86-speak).
*
* page_offset: The PAGE_OFFSET constant in the Guest kernel. We should
* probably wean the code off this, but it's a very useful constant! Any
* address above this is within the Guest kernel, and any kernel address can
* quickly converted from physical to virtual by adding PAGE_OFFSET. It's
* 0xC0000000 (3G) by default, but it's configurable at kernel build time.
*/
static int initialize(struct file *file, const u32 __user *input)
{
/* "struct lguest" contains everything we (the Host) know about a
* Guest. */
struct lguest *lg;
int err, i;
u32 args[4];
......@@ -111,7 +171,7 @@ static int initialize(struct file *file, const u32 __user *input)
/* We grab the Big Lguest lock, which protects the global array
* "lguests" and multiple simultaneous initializations. */
mutex_lock(&lguest_lock);
/* You can't initialize twice! Close the device and start again... */
if (file->private_data) {
err = -EBUSY;
goto unlock;
......@@ -122,37 +182,70 @@ static int initialize(struct file *file, const u32 __user *input)
goto unlock;
}
/* Find an unused guest. */
i = find_free_guest();
if (i < 0) {
err = -ENOSPC;
goto unlock;
}
/* OK, we have an index into the "lguest" array: "lg" is a convenient
* pointer. */
lg = &lguests[i];
/* Populate the easy fields of our "struct lguest" */
lg->guestid = i;
lg->pfn_limit = args[0];
lg->page_offset = args[3];
/* We need a complete page for the Guest registers: they are accessible
* to the Guest and we can only grant it access to whole pages. */
lg->regs_page = get_zeroed_page(GFP_KERNEL);
if (!lg->regs_page) {
err = -ENOMEM;
goto release_guest;
}
/* We actually put the registers at the bottom of the page. */
lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs);
/* Initialize the Guest's shadow page tables, using the toplevel
* address the Launcher gave us. This allocates memory, so can
* fail. */
err = init_guest_pagetable(lg, args[1]);
if (err)
goto free_regs;
/* Now we initialize the Guest's registers, handing it the start
* address. */
setup_regs(lg->regs, args[2]);
/* There are a couple of GDT entries the Guest expects when first
* booting. */
setup_guest_gdt(lg);
/* The timer for lguest's clock needs initialization. */
init_clockdev(lg);
/* We keep a pointer to the Launcher task (ie. current task) for when
* other Guests want to wake this one (inter-Guest I/O). */
lg->tsk = current;
/* We need to keep a pointer to the Launcher's memory map, because if
* the Launcher dies we need to clean it up. If we don't keep a
* reference, it is destroyed before close() is called. */
lg->mm = get_task_mm(lg->tsk);
/* Initialize the queue for the waker to wait on */
init_waitqueue_head(&lg->break_wq);
/* We remember which CPU's pages this Guest used last, for optimization
* when the same Guest runs on the same CPU twice. */
lg->last_pages = NULL;
/* We keep our "struct lguest" in the file's private_data. */
file->private_data = lg;
mutex_unlock(&lguest_lock);
/* And because this is a write() call, we return the length used. */
return sizeof(args);
free_regs:
......@@ -164,9 +257,15 @@ static int initialize(struct file *file, const u32 __user *input)
return err;
}
/*L:010 The first operation the Launcher does must be a write. All writes
* start with a 32 bit number: for the first write this must be
* LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use
* writes of other values to get DMA buffers and send interrupts. */
static ssize_t write(struct file *file, const char __user *input,
size_t size, loff_t *off)
{
/* Once the guest is initialized, we hold the "struct lguest" in the
* file private data. */
struct lguest *lg = file->private_data;
u32 req;
......@@ -174,8 +273,11 @@ static ssize_t write(struct file *file, const char __user *input,
return -EFAULT;
input += sizeof(req);
/* If you haven't initialized, you must do that first. */
if (req != LHREQ_INITIALIZE && !lg)
return -EINVAL;
/* Once the Guest is dead, all you can do is read() why it died. */
if (lg && lg->dead)
return -ENOENT;
......@@ -197,33 +299,72 @@ static ssize_t write(struct file *file, const char __user *input,
}
}
/*L:060 The final piece of interface code is the close() routine. It reverses
* everything done in initialize(). This is usually called because the
* Launcher exited.
*
* Note that the close routine returns 0 or a negative error number: it can't
* really fail, but it can whine. I blame Sun for this wart, and K&R C for
* letting them do it. :*/
static int close(struct inode *inode, struct file *file)
{
struct lguest *lg = file->private_data;
/* If we never successfully initialized, there's nothing to clean up */
if (!lg)
return 0;
/* We need the big lock, to protect from inter-guest I/O and other
* Launchers initializing guests. */
mutex_lock(&lguest_lock);
/* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
hrtimer_cancel(&lg->hrt);
/* Free any DMA buffers the Guest had bound. */
release_all_dma(lg);
/* Free up the shadow page tables for the Guest. */
free_guest_pagetable(lg);
/* Now all the memory cleanups are done, it's safe to release the
* Launcher's memory management structure. */
mmput(lg->mm);
/* If lg->dead doesn't contain an error code it will be NULL or a
* kmalloc()ed string, either of which is ok to hand to kfree(). */
if (!IS_ERR(lg->dead))
kfree(lg->dead);
/* We can free up the register page we allocated. */
free_page(lg->regs_page);
/* We clear the entire structure, which also marks it as free for the
* next user. */
memset(lg, 0, sizeof(*lg));
/* Release lock and exit. */
mutex_unlock(&lguest_lock);
return 0;
}
/*L:000
* Welcome to our journey through the Launcher!
*
* The Launcher is the Host userspace program which sets up, runs and services
* the Guest. In fact, many comments in the Drivers which refer to "the Host"
* doing things are inaccurate: the Launcher does all the device handling for
* the Guest. The Guest can't tell what's done by the the Launcher and what by
* the Host.
*
* Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
* shall see more of that later.
*
* We begin our understanding with the Host kernel interface which the Launcher
* uses: reading and writing a character device called /dev/lguest. All the
* work happens in the read(), write() and close() routines: */
static struct file_operations lguest_fops = {
.owner = THIS_MODULE,
.release = close,
.write = write,
.read = read,
};
/* This is a textbook example of a "misc" character device. Populate a "struct
* miscdevice" and register it with misc_register(). */
static struct miscdevice lguest_dev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "lguest",
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7