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  1. 26 Sep, 2020 6 commits
    • Nick Desaulniers's avatar
      lib/string.c: implement stpcpy · 1e1b6d63
      Nick Desaulniers authored 
      LLVM implemented a recent "libcall optimization" that lowers calls to
`sprintf(dest, "%s", str)` where the return value is used to
`stpcpy(dest, str) - dest`.

This generally avoids the machinery involved in parsing format strings.
`stpcpy` is just like `strcpy` except it returns the pointer to the new
tail of `dest`.  This optimization was introduced into clang-12.

Implement this so that we don't observe linkage failures due to missing
symbol definitions for `stpcpy`.

Similar to last year's fire drill with: commit 5f074f3e
("lib/string.c: implement a basic bcmp")

The kernel is somewhere between a "freestanding" environment (no full
libc) and "hosted" environment (many symbols from libc exist with the
same type, function signature, and semantics).

As Peter Anvin notes, there's not really a great way to inform the
compiler that you're targeting a freestanding environment but would like
to opt-in to some libcall optimizations (see pr/47280 below), rather
than opt-out.

Arvind notes, -fno-builtin-* behaves slightly differently between GCC
and Clang, and Clang is missing many __builtin_* definitions, which I
consider a bug in Clang and am working on fixing.

Masahiro summarizes the subtle distinction between compilers justly:
  To prevent transformation from foo() into bar(), there are two ways in
  Clang to do that; -fno-builtin-foo, and -fno-builtin-bar.  There is
  only one in GCC; -fno-buitin-foo.

(Any difference in that behavior in Clang is likely a bug from a missing
__builtin_* definition.)

Masahiro also notes:
  We want to disable optimization from foo() to bar(),
  but we may still benefit from the optimization from
  foo() into something else. If GCC implements the same transform, we
  would run into a problem because it is not -fno-builtin-bar, but
  -fno-builtin-foo that disables that optimization.

  In this regard, -fno-builtin-foo would be more future-proof than
  -fno-built-bar, but -fno-builtin-foo is still potentially overkill. We
  may want to prevent calls from foo() being optimized into calls to
  bar(), but we still may want other optimization on calls to foo().

It seems that compilers today don't quite provide the fine grain control
over which libcall optimizations pseudo-freestanding environments would
prefer.

Finally, Kees notes that this interface is unsafe, so we should not
encourage its use.  As such, I've removed the declaration from any
header, but it still needs to be exported to avoid linkage errors in
modules.
Reported-by: default avatarSami Tolvanen <samitolvanen@google.com>
Suggested-by: default avatarAndy Lavr <andy.lavr@gmail.com>
Suggested-by: default avatarArvind Sankar <nivedita@alum.mit.edu>
Suggested-by: default avatarJoe Perches <joe@perches.com>
Suggested-by: default avatarKees Cook <keescook@chromium.org>
Suggested-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Suggested-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Tested-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20200914161643.938408-1-ndesaulniers@google.com
Link: https://bugs.llvm.org/show_bug.cgi?id=47162
Link: https://bugs.llvm.org/show_bug.cgi?id=47280
Link: https://github.com/ClangBuiltLinux/linux/issues/1126
Link: https://man7.org/linux/man-pages/man3/stpcpy.3.html
Link: https://pubs.opengroup.org/onlinepubs/9699919799/functions/stpcpy.html
Link: https://reviews.llvm.org/D85963Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      1e1b6d63
    • Zi Yan's avatar
      mm/migrate: correct thp migration stats · 6c5c7b9f
      Zi Yan authored 
      PageTransHuge returns true for both thp and hugetlb, so thp stats was
counting both thp and hugetlb migrations.  Exclude hugetlb migration by
setting is_thp variable right.

Clean up thp handling code too when we are there.

Fixes: 1a5bae25 ("mm/vmstat: add events for THP migration without split")
Signed-off-by: default avatarZi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarDaniel Jordan <daniel.m.jordan@oracle.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lkml.kernel.org/r/20200917210413.1462975-1-zi.yan@sent.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      6c5c7b9f
    • Vasily Gorbik's avatar
      mm/gup: fix gup_fast with dynamic page table folding · d3f7b1bb
      Vasily Gorbik authored 
      Currently to make sure that every page table entry is read just once
gup_fast walks perform READ_ONCE and pass pXd value down to the next
gup_pXd_range function by value e.g.:

  static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end,
                           unsigned int flags, struct page **pages, int *nr)
  ...
          pudp = pud_offset(&p4d, addr);

This function passes a reference on that local value copy to pXd_offset,
and might get the very same pointer in return.  This happens when the
level is folded (on most arches), and that pointer should not be
iterated.

On s390 due to the fact that each task might have different 5,4 or
3-level address translation and hence different levels folded the logic
is more complex and non-iteratable pointer to a local copy leads to
severe problems.

Here is an example of what happens with gup_fast on s390, for a task
with 3-level paging, crossing a 2 GB pud boundary:

  // addr = 0x1007ffff000, end = 0x10080001000
  static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end,
                           unsigned int flags, struct page **pages, int *nr)
  {
        unsigned long next;
        pud_t *pudp;

        // pud_offset returns &p4d itself (a pointer to a value on stack)
        pudp = pud_offset(&p4d, addr);
        do {
                // on second iteratation reading "random" stack value
                pud_t pud = READ_ONCE(*pudp);

                // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390
                next = pud_addr_end(addr, end);
                ...
        } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack

        return 1;
  }

This happens since s390 moved to common gup code with commit
d1874a0c ("s390/mm: make the pxd_offset functions more robust") and
commit 1a42010c ("s390/mm: convert to the generic
get_user_pages_fast code").

s390 tried to mimic static level folding by changing pXd_offset
primitives to always calculate top level page table offset in pgd_offset
and just return the value passed when pXd_offset has to act as folded.

What is crucial for gup_fast and what has been overlooked is that
PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly.
And the latter is not possible with dynamic folding.

To fix the issue in addition to pXd values pass original pXdp pointers
down to gup_pXd_range functions.  And introduce pXd_offset_lockless
helpers, which take an additional pXd entry value parameter.  This has
already been discussed in

  https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1

Fixes: 1a42010c ("s390/mm: convert to the generic get_user_pages_fast code")
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarGerald Schaefer <gerald.schaefer@linux.ibm.com>
Reviewed-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Reviewed-by: default avatarMike Rapoport <rppt@linux.ibm.com>
Reviewed-by: default avatarJohn Hubbard <jhubbard@nvidia.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: <stable@vger.kernel.org>	[5.2+]
Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hoursSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      d3f7b1bb
    • Muchun Song's avatar
      mm: memcontrol: fix missing suffix of workingset_restore · 8d3fe09d
      Muchun Song authored 
      We forget to add the suffix to the workingset_restore string, so fix it.

And also update the documentation of cgroup-v2.rst.

Fixes: 170b04b7 ("mm/workingset: prepare the workingset detection infrastructure for anon LRU")
Signed-off-by: default avatarMuchun Song <songmuchun@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: https://lkml.kernel.org/r/20200916100030.71698-1-songmuchun@bytedance.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      8d3fe09d
    • Gao Xiang's avatar
      mm, THP, swap: fix allocating cluster for swapfile by mistake · 41663430
      Gao Xiang authored 
      SWP_FS is used to make swap_{read,write}page() go through the
filesystem, and it's only used for swap files over NFS.  So, !SWP_FS
means non NFS for now, it could be either file backed or device backed.
Something similar goes with legacy SWP_FILE.

So in order to achieve the goal of the original patch, SWP_BLKDEV should
be used instead.

FS corruption can be observed with SSD device + XFS + fragmented
swapfile due to CONFIG_THP_SWAP=y.

I reproduced the issue with the following details:

Environment:

  QEMU + upstream kernel + buildroot + NVMe (2 GB)

Kernel config:

  CONFIG_BLK_DEV_NVME=y
  CONFIG_THP_SWAP=y

Some reproducible steps:

  mkfs.xfs -f /dev/nvme0n1
  mkdir /tmp/mnt
  mount /dev/nvme0n1 /tmp/mnt
  bs="32k"
  sz="1024m"    # doesn't matter too much, I also tried 16m
  xfs_io -f -c "pwrite -R -b $bs 0 $sz" -c "fdatasync" /tmp/mnt/sw
  xfs_io -f -c "pwrite -R -b $bs 0 $sz" -c "fdatasync" /tmp/mnt/sw
  xfs_io -f -c "pwrite -R -b $bs 0 $sz" -c "fdatasync" /tmp/mnt/sw
  xfs_io -f -c "pwrite -F -S 0 -b $bs 0 $sz" -c "fdatasync" /tmp/mnt/sw
  xfs_io -f -c "pwrite -R -b $bs 0 $sz" -c "fsync" /tmp/mnt/sw

  mkswap /tmp/mnt/sw
  swapon /tmp/mnt/sw

  stress --vm 2 --vm-bytes 600M   # doesn't matter too much as well

Symptoms:
 - FS corruption (e.g. checksum failure)
 - memory corruption at: 0xd2808010
 - segfault

Fixes: f0eea189 ("mm, THP, swap: Don't allocate huge cluster for file backed swap device")
Fixes: 38d8b4e6 ("mm, THP, swap: delay splitting THP during swap out")
Signed-off-by: default avatarGao Xiang <hsiangkao@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatar"Huang, Ying" <ying.huang@intel.com>
Reviewed-by: default avatarYang Shi <shy828301@gmail.com>
Acked-by: default avatarRafael Aquini <aquini@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Eric Sandeen <esandeen@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20200820045323.7809-1-hsiangkao@redhat.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      41663430
    • Linus Torvalds's avatar
      Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm · 7c7ec322
      Linus Torvalds authored 
      Pull more kvm fixes from Paolo Bonzini:
 "Five small fixes.

  The nested migration bug will be fixed with a better API in 5.10 or
  5.11, for now this is a fix that works with existing userspace but
  keeps the current ugly API"

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  KVM: SVM: Add a dedicated INVD intercept routine
  KVM: x86: Reset MMU context if guest toggles CR4.SMAP or CR4.PKE
  KVM: x86: fix MSR_IA32_TSC read for nested migration
  selftests: kvm: Fix assert failure in single-step test
  KVM: x86: VMX: Make smaller physical guest address space support user-configurable
      7c7ec322
  3. 25 Sep, 2020 15 commits
  5. 24 Sep, 2020 6 commits
  7. 23 Sep, 2020 13 commits
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