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mm/migrate: Trylock device page in do_swap_page

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Avoid multiple CPU page faults to the same device page racing by trying
to lock the page in do_swap_page before taking an extra reference to the
page. This prevents scenarios where multiple CPU page faults each take
an extra reference to a device page, which could abort migration in
folio_migrate_mapping. With the device page being locked in
do_swap_page, the migrate_vma_* functions need to be updated to avoid
locking the fault_page argument.

Prior to this change, a livelock scenario could occur in Xe's (Intel GPU
DRM driver) SVM implementation if enough threads faulted the same device
page.

v3:
 - Put page after unlocking page (Alistair)
 - Warn on spliting a TPH which is fault page (Alistair)
 - Warn on dst page == fault page (Alistair)
v6:
 - Add more verbose comment around THP (Alistair)
v7:
 - Fix migrate_device_finalize alignment (Checkpatch)

Cc: Alistair Popple <apopple@nvidia.com>
Cc: Philip Yang <Philip.Yang@amd.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Simona Vetter <simona.vetter@ffwll.ch>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Tested-by: Alistair Popple <apopple@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250306012657.3505757-4-matthew.brost@intel.com
This commit is contained in:
Matthew Brost 2025-03-05 17:26:28 -08:00
parent a14fa8ec9d
commit 1afaeb8293
2 changed files with 55 additions and 22 deletions
Download patch file Download diff file Expand all files Collapse all files

13
mm/memory.c
View file

@ -4348,10 +4348,15 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
* Get a page reference while we know the page can't be
* freed.
*/
get_page(vmf->page);
pte_unmap_unlock(vmf->pte, vmf->ptl);
ret = vmf->page->pgmap->ops->migrate_to_ram(vmf);
put_page(vmf->page);
if (trylock_page(vmf->page)) {
get_page(vmf->page);
pte_unmap_unlock(vmf->pte, vmf->ptl);
ret = vmf->page->pgmap->ops->migrate_to_ram(vmf);
unlock_page(vmf->page);
put_page(vmf->page);
} else {
pte_unmap_unlock(vmf->pte, vmf->ptl);
}
} else if (is_hwpoison_entry(entry)) {
ret = VM_FAULT_HWPOISON;
} else if (is_pte_marker_entry(entry)) {

64
mm/migrate_device.c
View file

@ -60,6 +60,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
struct mm_walk *walk)
{
struct migrate_vma *migrate = walk->private;
struct folio *fault_folio = migrate->fault_page ?
page_folio(migrate->fault_page) : NULL;
struct vm_area_struct *vma = walk->vma;
struct mm_struct *mm = vma->vm_mm;
unsigned long addr = start, unmapped = 0;
@ -88,11 +90,16 @@ again:
folio_get(folio);
spin_unlock(ptl);
/* FIXME: we don't expect THP for fault_folio */
if (WARN_ON_ONCE(fault_folio == folio))
return migrate_vma_collect_skip(start, end,
walk);
if (unlikely(!folio_trylock(folio)))
return migrate_vma_collect_skip(start, end,
walk);
ret = split_folio(folio);
folio_unlock(folio);
if (fault_folio != folio)
folio_unlock(folio);
folio_put(folio);
if (ret)
return migrate_vma_collect_skip(start, end,
@ -192,7 +199,7 @@ again:
* optimisation to avoid walking the rmap later with
* try_to_migrate().
*/
if (folio_trylock(folio)) {
if (fault_folio == folio || folio_trylock(folio)) {
bool anon_exclusive;
pte_t swp_pte;
@ -204,7 +211,8 @@ again:
if (folio_try_share_anon_rmap_pte(folio, page)) {
set_pte_at(mm, addr, ptep, pte);
folio_unlock(folio);
if (fault_folio != folio)
folio_unlock(folio);
folio_put(folio);
mpfn = 0;
goto next;
@ -363,6 +371,8 @@ static unsigned long migrate_device_unmap(unsigned long *src_pfns,
unsigned long npages,
struct page *fault_page)
{
struct folio *fault_folio = fault_page ?
page_folio(fault_page) : NULL;
unsigned long i, restore = 0;
bool allow_drain = true;
unsigned long unmapped = 0;
@ -427,7 +437,8 @@ static unsigned long migrate_device_unmap(unsigned long *src_pfns,
remove_migration_ptes(folio, folio, 0);
src_pfns[i] = 0;
folio_unlock(folio);
if (fault_folio != folio)
folio_unlock(folio);
folio_put(folio);
restore--;
}
@ -536,6 +547,8 @@ int migrate_vma_setup(struct migrate_vma *args)
return -EINVAL;
if (args->fault_page && !is_device_private_page(args->fault_page))
return -EINVAL;
if (args->fault_page && !PageLocked(args->fault_page))
return -EINVAL;
memset(args->src, 0, sizeof(*args->src) * nr_pages);
args->cpages = 0;
@ -799,19 +812,13 @@ void migrate_vma_pages(struct migrate_vma *migrate)
}
EXPORT_SYMBOL(migrate_vma_pages);
/*
* migrate_device_finalize() - complete page migration
* @src_pfns: src_pfns returned from migrate_device_range()
* @dst_pfns: array of pfns allocated by the driver to migrate memory to
* @npages: number of pages in the range
*
* Completes migration of the page by removing special migration entries.
* Drivers must ensure copying of page data is complete and visible to the CPU
* before calling this.
*/
void migrate_device_finalize(unsigned long *src_pfns,
unsigned long *dst_pfns, unsigned long npages)
static void __migrate_device_finalize(unsigned long *src_pfns,
unsigned long *dst_pfns,
unsigned long npages,
struct page *fault_page)
{
struct folio *fault_folio = fault_page ?
page_folio(fault_page) : NULL;
unsigned long i;
for (i = 0; i < npages; i++) {
@ -824,6 +831,7 @@ void migrate_device_finalize(unsigned long *src_pfns,
if (!page) {
if (dst) {
WARN_ON_ONCE(fault_folio == dst);
folio_unlock(dst);
folio_put(dst);
}
@ -834,6 +842,7 @@ void migrate_device_finalize(unsigned long *src_pfns,
if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE) || !dst) {
if (dst) {
WARN_ON_ONCE(fault_folio == dst);
folio_unlock(dst);
folio_put(dst);
}
@ -843,15 +852,33 @@ void migrate_device_finalize(unsigned long *src_pfns,
if (!folio_is_zone_device(dst))
folio_add_lru(dst);
remove_migration_ptes(src, dst, 0);
folio_unlock(src);
if (fault_folio != src)
folio_unlock(src);
folio_put(src);
if (dst != src) {
WARN_ON_ONCE(fault_folio == dst);
folio_unlock(dst);
folio_put(dst);
}
}
}
/*
* migrate_device_finalize() - complete page migration
* @src_pfns: src_pfns returned from migrate_device_range()
* @dst_pfns: array of pfns allocated by the driver to migrate memory to
* @npages: number of pages in the range
*
* Completes migration of the page by removing special migration entries.
* Drivers must ensure copying of page data is complete and visible to the CPU
* before calling this.
*/
void migrate_device_finalize(unsigned long *src_pfns,
unsigned long *dst_pfns, unsigned long npages)
{
return __migrate_device_finalize(src_pfns, dst_pfns, npages, NULL);
}
EXPORT_SYMBOL(migrate_device_finalize);
/**
@ -867,7 +894,8 @@ EXPORT_SYMBOL(migrate_device_finalize);
*/
void migrate_vma_finalize(struct migrate_vma *migrate)
{
migrate_device_finalize(migrate->src, migrate->dst, migrate->npages);
__migrate_device_finalize(migrate->src, migrate->dst, migrate->npages,
migrate->fault_page);
}
EXPORT_SYMBOL(migrate_vma_finalize);