Commit d6aca350 authored by Juergen Gross's avatar Juergen Gross

xen/grant-dma-ops: Add option to restrict memory access under Xen

Introduce Xen grant DMA-mapping layer which contains special DMA-mapping
routines for providing grant references as DMA addresses to be used by
frontends (e.g. virtio) in Xen guests.

Add the needed functionality by providing a special set of DMA ops
handling the needed grant operations for the I/O pages.

The subsequent commit will introduce the use case for xen-grant DMA ops
layer to enable using virtio devices in Xen guests in a safe manner.
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarOleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: default avatarStefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/1654197833-25362-4-git-send-email-olekstysh@gmail.comSigned-off-by: default avatarJuergen Gross <jgross@suse.com>
parent 02a9e681
......@@ -335,4 +335,8 @@ config XEN_UNPOPULATED_ALLOC
having to balloon out RAM regions in order to obtain physical memory
space to create such mappings.
config XEN_GRANT_DMA_OPS
bool
select DMA_OPS
endmenu
......@@ -39,3 +39,4 @@ xen-gntalloc-y := gntalloc.o
xen-privcmd-y := privcmd.o privcmd-buf.o
obj-$(CONFIG_XEN_FRONT_PGDIR_SHBUF) += xen-front-pgdir-shbuf.o
obj-$(CONFIG_XEN_UNPOPULATED_ALLOC) += unpopulated-alloc.o
obj-$(CONFIG_XEN_GRANT_DMA_OPS) += grant-dma-ops.o
// SPDX-License-Identifier: GPL-2.0-only
/*
* Xen grant DMA-mapping layer - contains special DMA-mapping routines
* for providing grant references as DMA addresses to be used by frontends
* (e.g. virtio) in Xen guests
*
* Copyright (c) 2021, Juergen Gross <jgross@suse.com>
*/
#include <linux/module.h>
#include <linux/dma-map-ops.h>
#include <linux/of.h>
#include <linux/pfn.h>
#include <linux/xarray.h>
#include <xen/xen.h>
#include <xen/xen-ops.h>
#include <xen/grant_table.h>
struct xen_grant_dma_data {
/* The ID of backend domain */
domid_t backend_domid;
/* Is device behaving sane? */
bool broken;
};
static DEFINE_XARRAY(xen_grant_dma_devices);
#define XEN_GRANT_DMA_ADDR_OFF (1ULL << 63)
static inline dma_addr_t grant_to_dma(grant_ref_t grant)
{
return XEN_GRANT_DMA_ADDR_OFF | ((dma_addr_t)grant << PAGE_SHIFT);
}
static inline grant_ref_t dma_to_grant(dma_addr_t dma)
{
return (grant_ref_t)((dma & ~XEN_GRANT_DMA_ADDR_OFF) >> PAGE_SHIFT);
}
static struct xen_grant_dma_data *find_xen_grant_dma_data(struct device *dev)
{
struct xen_grant_dma_data *data;
xa_lock(&xen_grant_dma_devices);
data = xa_load(&xen_grant_dma_devices, (unsigned long)dev);
xa_unlock(&xen_grant_dma_devices);
return data;
}
/*
* DMA ops for Xen frontends (e.g. virtio).
*
* Used to act as a kind of software IOMMU for Xen guests by using grants as
* DMA addresses.
* Such a DMA address is formed by using the grant reference as a frame
* number and setting the highest address bit (this bit is for the backend
* to be able to distinguish it from e.g. a mmio address).
*
* Note that for now we hard wire dom0 to be the backend domain. In order
* to support any domain as backend we'd need to add a way to communicate
* the domid of this backend, e.g. via Xenstore, via the PCI-device's
* config space or DT/ACPI.
*/
static void *xen_grant_dma_alloc(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t gfp,
unsigned long attrs)
{
struct xen_grant_dma_data *data;
unsigned int i, n_pages = PFN_UP(size);
unsigned long pfn;
grant_ref_t grant;
void *ret;
data = find_xen_grant_dma_data(dev);
if (!data)
return NULL;
if (unlikely(data->broken))
return NULL;
ret = alloc_pages_exact(n_pages * PAGE_SIZE, gfp);
if (!ret)
return NULL;
pfn = virt_to_pfn(ret);
if (gnttab_alloc_grant_reference_seq(n_pages, &grant)) {
free_pages_exact(ret, n_pages * PAGE_SIZE);
return NULL;
}
for (i = 0; i < n_pages; i++) {
gnttab_grant_foreign_access_ref(grant + i, data->backend_domid,
pfn_to_gfn(pfn + i), 0);
}
*dma_handle = grant_to_dma(grant);
return ret;
}
static void xen_grant_dma_free(struct device *dev, size_t size, void *vaddr,
dma_addr_t dma_handle, unsigned long attrs)
{
struct xen_grant_dma_data *data;
unsigned int i, n_pages = PFN_UP(size);
grant_ref_t grant;
data = find_xen_grant_dma_data(dev);
if (!data)
return;
if (unlikely(data->broken))
return;
grant = dma_to_grant(dma_handle);
for (i = 0; i < n_pages; i++) {
if (unlikely(!gnttab_end_foreign_access_ref(grant + i))) {
dev_alert(dev, "Grant still in use by backend domain, disabled for further use\n");
data->broken = true;
return;
}
}
gnttab_free_grant_reference_seq(grant, n_pages);
free_pages_exact(vaddr, n_pages * PAGE_SIZE);
}
static struct page *xen_grant_dma_alloc_pages(struct device *dev, size_t size,
dma_addr_t *dma_handle,
enum dma_data_direction dir,
gfp_t gfp)
{
void *vaddr;
vaddr = xen_grant_dma_alloc(dev, size, dma_handle, gfp, 0);
if (!vaddr)
return NULL;
return virt_to_page(vaddr);
}
static void xen_grant_dma_free_pages(struct device *dev, size_t size,
struct page *vaddr, dma_addr_t dma_handle,
enum dma_data_direction dir)
{
xen_grant_dma_free(dev, size, page_to_virt(vaddr), dma_handle, 0);
}
static dma_addr_t xen_grant_dma_map_page(struct device *dev, struct page *page,
unsigned long offset, size_t size,
enum dma_data_direction dir,
unsigned long attrs)
{
struct xen_grant_dma_data *data;
unsigned int i, n_pages = PFN_UP(size);
grant_ref_t grant;
dma_addr_t dma_handle;
if (WARN_ON(dir == DMA_NONE))
return DMA_MAPPING_ERROR;
data = find_xen_grant_dma_data(dev);
if (!data)
return DMA_MAPPING_ERROR;
if (unlikely(data->broken))
return DMA_MAPPING_ERROR;
if (gnttab_alloc_grant_reference_seq(n_pages, &grant))
return DMA_MAPPING_ERROR;
for (i = 0; i < n_pages; i++) {
gnttab_grant_foreign_access_ref(grant + i, data->backend_domid,
xen_page_to_gfn(page) + i, dir == DMA_TO_DEVICE);
}
dma_handle = grant_to_dma(grant) + offset;
return dma_handle;
}
static void xen_grant_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
size_t size, enum dma_data_direction dir,
unsigned long attrs)
{
struct xen_grant_dma_data *data;
unsigned int i, n_pages = PFN_UP(size);
grant_ref_t grant;
if (WARN_ON(dir == DMA_NONE))
return;
data = find_xen_grant_dma_data(dev);
if (!data)
return;
if (unlikely(data->broken))
return;
grant = dma_to_grant(dma_handle);
for (i = 0; i < n_pages; i++) {
if (unlikely(!gnttab_end_foreign_access_ref(grant + i))) {
dev_alert(dev, "Grant still in use by backend domain, disabled for further use\n");
data->broken = true;
return;
}
}
gnttab_free_grant_reference_seq(grant, n_pages);
}
static void xen_grant_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
int nents, enum dma_data_direction dir,
unsigned long attrs)
{
struct scatterlist *s;
unsigned int i;
if (WARN_ON(dir == DMA_NONE))
return;
for_each_sg(sg, s, nents, i)
xen_grant_dma_unmap_page(dev, s->dma_address, sg_dma_len(s), dir,
attrs);
}
static int xen_grant_dma_map_sg(struct device *dev, struct scatterlist *sg,
int nents, enum dma_data_direction dir,
unsigned long attrs)
{
struct scatterlist *s;
unsigned int i;
if (WARN_ON(dir == DMA_NONE))
return -EINVAL;
for_each_sg(sg, s, nents, i) {
s->dma_address = xen_grant_dma_map_page(dev, sg_page(s), s->offset,
s->length, dir, attrs);
if (s->dma_address == DMA_MAPPING_ERROR)
goto out;
sg_dma_len(s) = s->length;
}
return nents;
out:
xen_grant_dma_unmap_sg(dev, sg, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
sg_dma_len(sg) = 0;
return -EIO;
}
static int xen_grant_dma_supported(struct device *dev, u64 mask)
{
return mask == DMA_BIT_MASK(64);
}
static const struct dma_map_ops xen_grant_dma_ops = {
.alloc = xen_grant_dma_alloc,
.free = xen_grant_dma_free,
.alloc_pages = xen_grant_dma_alloc_pages,
.free_pages = xen_grant_dma_free_pages,
.mmap = dma_common_mmap,
.get_sgtable = dma_common_get_sgtable,
.map_page = xen_grant_dma_map_page,
.unmap_page = xen_grant_dma_unmap_page,
.map_sg = xen_grant_dma_map_sg,
.unmap_sg = xen_grant_dma_unmap_sg,
.dma_supported = xen_grant_dma_supported,
};
void xen_grant_setup_dma_ops(struct device *dev)
{
struct xen_grant_dma_data *data;
data = find_xen_grant_dma_data(dev);
if (data) {
dev_err(dev, "Xen grant DMA data is already created\n");
return;
}
data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
if (!data)
goto err;
/* XXX The dom0 is hardcoded as the backend domain for now */
data->backend_domid = 0;
if (xa_err(xa_store(&xen_grant_dma_devices, (unsigned long)dev, data,
GFP_KERNEL))) {
dev_err(dev, "Cannot store Xen grant DMA data\n");
goto err;
}
dev->dma_ops = &xen_grant_dma_ops;
return;
err:
dev_err(dev, "Cannot set up Xen grant DMA ops, retain platform DMA ops\n");
}
MODULE_DESCRIPTION("Xen grant DMA-mapping layer");
MODULE_AUTHOR("Juergen Gross <jgross@suse.com>");
MODULE_LICENSE("GPL");
......@@ -214,4 +214,12 @@ static inline void xen_preemptible_hcall_end(void) { }
#endif /* CONFIG_XEN_PV && !CONFIG_PREEMPTION */
#ifdef CONFIG_XEN_GRANT_DMA_OPS
void xen_grant_setup_dma_ops(struct device *dev);
#else
static inline void xen_grant_setup_dma_ops(struct device *dev)
{
}
#endif /* CONFIG_XEN_GRANT_DMA_OPS */
#endif /* INCLUDE_XEN_OPS_H */
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