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xen/gntdev: Avoid blocking in unmap_grant_pages()

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unmap_grant_pages() currently waits for the pages to no longer be used.
In https://github.com/QubesOS/qubes-issues/issues/7481, this lead to a
deadlock against i915: i915 was waiting for gntdev's MMU notifier to
finish, while gntdev was waiting for i915 to free its pages.  I also
believe this is responsible for various deadlocks I have experienced in
the past.

Avoid these problems by making unmap_grant_pages async.  This requires
making it return void, as any errors will not be available when the
function returns.  Fortunately, the only use of the return value is a
WARN_ON(), which can be replaced by a WARN_ON when the error is
detected.  Additionally, a failed call will not prevent further calls
from being made, but this is harmless.

Because unmap_grant_pages is now async, the grant handle will be sent to
INVALID_GRANT_HANDLE too late to prevent multiple unmaps of the same
handle.  Instead, a separate bool array is allocated for this purpose.
This wastes memory, but stuffing this information in padding bytes is
too fragile.  Furthermore, it is necessary to grab a reference to the
map before making the asynchronous call, and release the reference when
the call returns.

It is also necessary to guard against reentrancy in gntdev_map_put(),
and to handle the case where userspace tries to map a mapping whose
contents have not all been freed yet.

Fixes: 745282256c ("xen/gntdev: safely unmap grants in case they are still in use")
Cc: stable@vger.kernel.org
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220622022726.2538-1-demi@invisiblethingslab.com
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Demi Marie Obenour 2022-06-21 22:27:26 -04:00 committed by Juergen Gross
parent ca6969013d
commit dbe97cff7d
2 changed files with 113 additions and 51 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
drivers/xen/gntdev-common.h
View File

@ -16,6 +16,7 @@
#include <linux/mmu_notifier.h>
#include <linux/types.h>
#include <xen/interface/event_channel.h>
#include <xen/grant_table.h>
struct gntdev_dmabuf_priv;
@ -56,6 +57,7 @@ struct gntdev_grant_map {
struct gnttab_unmap_grant_ref *unmap_ops;
struct gnttab_map_grant_ref *kmap_ops;
struct gnttab_unmap_grant_ref *kunmap_ops;
bool *being_removed;
struct page **pages;
unsigned long pages_vm_start;
@ -73,6 +75,11 @@ struct gntdev_grant_map {
/* Needed to avoid allocation in gnttab_dma_free_pages(). */
xen_pfn_t *frames;
#endif
/* Number of live grants */
atomic_t live_grants;
/* Needed to avoid allocation in __unmap_grant_pages */
struct gntab_unmap_queue_data unmap_data;
};
struct gntdev_grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count,

157
drivers/xen/gntdev.c
View File

@ -35,6 +35,7 @@
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/refcount.h>
#include <linux/workqueue.h>
#include <xen/xen.h>
#include <xen/grant_table.h>
@ -60,10 +61,11 @@ module_param(limit, uint, 0644);
MODULE_PARM_DESC(limit,
"Maximum number of grants that may be mapped by one mapping request");
/* True in PV mode, false otherwise */
static int use_ptemod;
static int unmap_grant_pages(struct gntdev_grant_map *map,
int offset, int pages);
static void unmap_grant_pages(struct gntdev_grant_map *map,
int offset, int pages);
static struct miscdevice gntdev_miscdev;
@ -120,6 +122,7 @@ static void gntdev_free_map(struct gntdev_grant_map *map)
kvfree(map->unmap_ops);
kvfree(map->kmap_ops);
kvfree(map->kunmap_ops);
kvfree(map->being_removed);
kfree(map);
}
@ -140,10 +143,13 @@ struct gntdev_grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count,
add->unmap_ops = kvmalloc_array(count, sizeof(add->unmap_ops[0]),
GFP_KERNEL);
add->pages = kvcalloc(count, sizeof(add->pages[0]), GFP_KERNEL);
add->being_removed =
kvcalloc(count, sizeof(add->being_removed[0]), GFP_KERNEL);
if (NULL == add->grants ||
NULL == add->map_ops ||
NULL == add->unmap_ops ||
NULL == add->pages)
NULL == add->pages ||
NULL == add->being_removed)
goto err;
if (use_ptemod) {
add->kmap_ops = kvmalloc_array(count, sizeof(add->kmap_ops[0]),
@ -250,9 +256,36 @@ void gntdev_put_map(struct gntdev_priv *priv, struct gntdev_grant_map *map)
if (!refcount_dec_and_test(&map->users))
return;
if (map->pages && !use_ptemod)
if (map->pages && !use_ptemod) {
/*
* Increment the reference count. This ensures that the
* subsequent call to unmap_grant_pages() will not wind up
* re-entering itself. It *can* wind up calling
* gntdev_put_map() recursively, but such calls will be with a
* reference count greater than 1, so they will return before
* this code is reached. The recursion depth is thus limited to
* 1. Do NOT use refcount_inc() here, as it will detect that
* the reference count is zero and WARN().
*/
refcount_set(&map->users, 1);
/*
* Unmap the grants. This may or may not be asynchronous, so it
* is possible that the reference count is 1 on return, but it
* could also be greater than 1.
*/
unmap_grant_pages(map, 0, map->count);
/* Check if the memory now needs to be freed */
if (!refcount_dec_and_test(&map->users))
return;
/*
* All pages have been returned to the hypervisor, so free the
* map.
*/
}
if (map->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
notify_remote_via_evtchn(map->notify.event);
evtchn_put(map->notify.event);
@ -283,6 +316,7 @@ static int find_grant_ptes(pte_t *pte, unsigned long addr, void *data)
int gntdev_map_grant_pages(struct gntdev_grant_map *map)
{
size_t alloced = 0;
int i, err = 0;
if (!use_ptemod) {
@ -331,97 +365,116 @@ int gntdev_map_grant_pages(struct gntdev_grant_map *map)
map->count);
for (i = 0; i < map->count; i++) {
if (map->map_ops[i].status == GNTST_okay)
if (map->map_ops[i].status == GNTST_okay) {
map->unmap_ops[i].handle = map->map_ops[i].handle;
else if (!err)
if (!use_ptemod)
alloced++;
} else if (!err)
err = -EINVAL;
if (map->flags & GNTMAP_device_map)
map->unmap_ops[i].dev_bus_addr = map->map_ops[i].dev_bus_addr;
if (use_ptemod) {
if (map->kmap_ops[i].status == GNTST_okay)
if (map->kmap_ops[i].status == GNTST_okay) {
if (map->map_ops[i].status == GNTST_okay)
alloced++;
map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
else if (!err)
} else if (!err)
err = -EINVAL;
}
}
atomic_add(alloced, &map->live_grants);
return err;
}
static int __unmap_grant_pages(struct gntdev_grant_map *map, int offset,
int pages)
static void __unmap_grant_pages_done(int result,
struct gntab_unmap_queue_data *data)
{
int i, err = 0;
struct gntab_unmap_queue_data unmap_data;
unsigned int i;
struct gntdev_grant_map *map = data->data;
unsigned int offset = data->unmap_ops - map->unmap_ops;
if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
int pgno = (map->notify.addr >> PAGE_SHIFT);
if (pgno >= offset && pgno < offset + pages) {
/* No need for kmap, pages are in lowmem */
uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno]));
tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
}
}
unmap_data.unmap_ops = map->unmap_ops + offset;
unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
unmap_data.pages = map->pages + offset;
unmap_data.count = pages;
err = gnttab_unmap_refs_sync(&unmap_data);
if (err)
return err;
for (i = 0; i < pages; i++) {
if (map->unmap_ops[offset+i].status)
err = -EINVAL;
for (i = 0; i < data->count; i++) {
WARN_ON(map->unmap_ops[offset+i].status);
pr_debug("unmap handle=%d st=%d\n",
map->unmap_ops[offset+i].handle,
map->unmap_ops[offset+i].status);
map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
if (use_ptemod) {
if (map->kunmap_ops[offset+i].status)
err = -EINVAL;
WARN_ON(map->kunmap_ops[offset+i].status);
pr_debug("kunmap handle=%u st=%d\n",
map->kunmap_ops[offset+i].handle,
map->kunmap_ops[offset+i].status);
map->kunmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
}
}
return err;
/*
* Decrease the live-grant counter. This must happen after the loop to
* prevent premature reuse of the grants by gnttab_mmap().
*/
atomic_sub(data->count, &map->live_grants);
/* Release reference taken by __unmap_grant_pages */
gntdev_put_map(NULL, map);
}
static int unmap_grant_pages(struct gntdev_grant_map *map, int offset,
int pages)
static void __unmap_grant_pages(struct gntdev_grant_map *map, int offset,
int pages)
{
int range, err = 0;
if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
int pgno = (map->notify.addr >> PAGE_SHIFT);
if (pgno >= offset && pgno < offset + pages) {
/* No need for kmap, pages are in lowmem */
uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno]));
tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
}
}
map->unmap_data.unmap_ops = map->unmap_ops + offset;
map->unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
map->unmap_data.pages = map->pages + offset;
map->unmap_data.count = pages;
map->unmap_data.done = __unmap_grant_pages_done;
map->unmap_data.data = map;
refcount_inc(&map->users); /* to keep map alive during async call below */
gnttab_unmap_refs_async(&map->unmap_data);
}
static void unmap_grant_pages(struct gntdev_grant_map *map, int offset,
int pages)
{
int range;
if (atomic_read(&map->live_grants) == 0)
return; /* Nothing to do */
pr_debug("unmap %d+%d [%d+%d]\n", map->index, map->count, offset, pages);
/* It is possible the requested range will have a "hole" where we
* already unmapped some of the grants. Only unmap valid ranges.
*/
while (pages && !err) {
while (pages &&
map->unmap_ops[offset].handle == INVALID_GRANT_HANDLE) {
while (pages) {
while (pages && map->being_removed[offset]) {
offset++;
pages--;
}
range = 0;
while (range < pages) {
if (map->unmap_ops[offset + range].handle ==
INVALID_GRANT_HANDLE)
if (map->being_removed[offset + range])
break;
map->being_removed[offset + range] = true;
range++;
}
err = __unmap_grant_pages(map, offset, range);
if (range)
__unmap_grant_pages(map, offset, range);
offset += range;
pages -= range;
}
return err;
}
/* ------------------------------------------------------------------ */
@ -473,7 +526,6 @@ static bool gntdev_invalidate(struct mmu_interval_notifier *mn,
struct gntdev_grant_map *map =
container_of(mn, struct gntdev_grant_map, notifier);
unsigned long mstart, mend;
int err;
if (!mmu_notifier_range_blockable(range))
return false;
@ -494,10 +546,9 @@ static bool gntdev_invalidate(struct mmu_interval_notifier *mn,
map->index, map->count,
map->vma->vm_start, map->vma->vm_end,
range->start, range->end, mstart, mend);
err = unmap_grant_pages(map,
unmap_grant_pages(map,
(mstart - map->vma->vm_start) >> PAGE_SHIFT,
(mend - mstart) >> PAGE_SHIFT);
WARN_ON(err);
return true;
}
@ -985,6 +1036,10 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
goto unlock_out;
if (use_ptemod && map->vma)
goto unlock_out;
if (atomic_read(&map->live_grants)) {
err = -EAGAIN;
goto unlock_out;
}
refcount_inc(&map->users);
vma->vm_ops = &gntdev_vmops;