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mm/rmap: handle device-exclusive entries correctly in try_to_migrate_one()

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Ever since commit b756a3b5e7 ("mm: device exclusive memory access") we
can return with a device-exclusive entry from page_vma_mapped_walk().

try_to_migrate_one() is not prepared for that, so teach it about these PFN
swap PTEs.  We already handle device-private entries by specializing on
the folio, so we can reshuffle that code to make it work on the PFN swap
PTEs instead.

Get rid of the folio_is_device_private() handling.  Note that we never
currently expect device-private folios with HWPoison flag set at that
point, so add a warning in case that ever changes and we can figure out
what the right thing to do is.

Note that we could currently only run into this case with device-exclusive
entries on THPs.  We still adjust the mapcount on conversion to
device-exclusive; this makes the rmap walk abort early for small folios,
because we'll always have !folio_mapped() with a single device-exclusive
entry.  We'll adjust the mapcount logic once all page_vma_mapped_walk()
users can properly handle device-exclusive entries.

Further note that try_to_migrate() calls MMU notifiers and holds the folio
lock, so any device-exclusive users should be properly prepared for a
device-exclusive PTE to "vanish".

Link: https://lkml.kernel.org/r/20250210193801.781278-12-david@redhat.com
Fixes: b756a3b5e7 ("mm: device exclusive memory access")
Signed-off-by: David Hildenbrand <david@redhat.com>
Tested-by: Alistair Popple <apopple@nvidia.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Lyude <lyude@redhat.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Simona Vetter <simona.vetter@ffwll.ch>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yanteng Si <si.yanteng@linux.dev>
Cc: Barry Song <v-songbaohua@oppo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2025-02-10 20:37:53 +01:00 committed by Andrew Morton
parent 6552929560
commit bf983108be
1 changed files with 51 additions and 73 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

124
mm/rmap.c
View File

@ -2039,9 +2039,9 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
{
struct mm_struct *mm = vma->vm_mm;
DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
bool anon_exclusive, writable, ret = true;
pte_t pteval;
struct page *subpage;
bool anon_exclusive, ret = true;
struct mmu_notifier_range range;
enum ttu_flags flags = (enum ttu_flags)(long)arg;
unsigned long pfn;
@ -2108,24 +2108,19 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
/* Unexpected PMD-mapped THP? */
VM_BUG_ON_FOLIO(!pvmw.pte, folio);
pfn = pte_pfn(ptep_get(pvmw.pte));
if (folio_is_zone_device(folio)) {
/*
* Our PTE is a non-present device exclusive entry and
* calculating the subpage as for the common case would
* result in an invalid pointer.
*
* Since only PAGE_SIZE pages can currently be
* migrated, just set it to page. This will need to be
* changed when hugepage migrations to device private
* memory are supported.
*/
VM_BUG_ON_FOLIO(folio_nr_pages(folio) > 1, folio);
subpage = &folio->page;
/*
* Handle PFN swap PTEs, such as device-exclusive ones, that
* actually map pages.
*/
pteval = ptep_get(pvmw.pte);
if (likely(pte_present(pteval))) {
pfn = pte_pfn(pteval);
} else {
subpage = folio_page(folio, pfn - folio_pfn(folio));
pfn = swp_offset_pfn(pte_to_swp_entry(pteval));
VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
}
subpage = folio_page(folio, pfn - folio_pfn(folio));
address = pvmw.address;
anon_exclusive = folio_test_anon(folio) &&
PageAnonExclusive(subpage);
@ -2181,7 +2176,10 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
}
/* Nuke the hugetlb page table entry */
pteval = huge_ptep_clear_flush(vma, address, pvmw.pte);
} else {
if (pte_dirty(pteval))
folio_mark_dirty(folio);
writable = pte_write(pteval);
} else if (likely(pte_present(pteval))) {
flush_cache_page(vma, address, pfn);
/* Nuke the page table entry. */
if (should_defer_flush(mm, flags)) {
@ -2199,54 +2197,23 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
} else {
pteval = ptep_clear_flush(vma, address, pvmw.pte);
}
if (pte_dirty(pteval))
folio_mark_dirty(folio);
writable = pte_write(pteval);
} else {
pte_clear(mm, address, pvmw.pte);
writable = is_writable_device_private_entry(pte_to_swp_entry(pteval));
}
/* Set the dirty flag on the folio now the pte is gone. */
if (pte_dirty(pteval))
folio_mark_dirty(folio);
VM_WARN_ON_FOLIO(writable && folio_test_anon(folio) &&
!anon_exclusive, folio);
/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
if (folio_is_device_private(folio)) {
unsigned long pfn = folio_pfn(folio);
swp_entry_t entry;
pte_t swp_pte;
if (PageHWPoison(subpage)) {
VM_WARN_ON_FOLIO(folio_is_device_private(folio), folio);
if (anon_exclusive)
WARN_ON_ONCE(folio_try_share_anon_rmap_pte(folio,
subpage));
/*
* Store the pfn of the page in a special migration
* pte. do_swap_page() will wait until the migration
* pte is removed and then restart fault handling.
*/
entry = pte_to_swp_entry(pteval);
if (is_writable_device_private_entry(entry))
entry = make_writable_migration_entry(pfn);
else if (anon_exclusive)
entry = make_readable_exclusive_migration_entry(pfn);
else
entry = make_readable_migration_entry(pfn);
swp_pte = swp_entry_to_pte(entry);
/*
* pteval maps a zone device page and is therefore
* a swap pte.
*/
if (pte_swp_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_swp_uffd_wp(pteval))
swp_pte = pte_swp_mkuffd_wp(swp_pte);
set_pte_at(mm, pvmw.address, pvmw.pte, swp_pte);
trace_set_migration_pte(pvmw.address, pte_val(swp_pte),
folio_order(folio));
/*
* No need to invalidate here it will synchronize on
* against the special swap migration pte.
*/
} else if (PageHWPoison(subpage)) {
pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
if (folio_test_hugetlb(folio)) {
hugetlb_count_sub(folio_nr_pages(folio), mm);
@ -2256,8 +2223,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
dec_mm_counter(mm, mm_counter(folio));
set_pte_at(mm, address, pvmw.pte, pteval);
}
} else if (pte_unused(pteval) && !userfaultfd_armed(vma)) {
} else if (likely(pte_present(pteval)) && pte_unused(pteval) &&
!userfaultfd_armed(vma)) {
/*
* The guest indicated that the page content is of no
* interest anymore. Simply discard the pte, vmscan
@ -2273,6 +2240,11 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
swp_entry_t entry;
pte_t swp_pte;
/*
* arch_unmap_one() is expected to be a NOP on
* architectures where we could have PFN swap PTEs,
* so we'll not check/care.
*/
if (arch_unmap_one(mm, vma, address, pteval) < 0) {
if (folio_test_hugetlb(folio))
set_huge_pte_at(mm, address, pvmw.pte,
@ -2283,8 +2255,6 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
page_vma_mapped_walk_done(&pvmw);
break;
}
VM_BUG_ON_PAGE(pte_write(pteval) && folio_test_anon(folio) &&
!anon_exclusive, subpage);
/* See folio_try_share_anon_rmap_pte(): clear PTE first. */
if (folio_test_hugetlb(folio)) {
@ -2309,7 +2279,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
* pte. do_swap_page() will wait until the migration
* pte is removed and then restart fault handling.
*/
if (pte_write(pteval))
if (writable)
entry = make_writable_migration_entry(
page_to_pfn(subpage));
else if (anon_exclusive)
@ -2318,15 +2288,23 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
else
entry = make_readable_migration_entry(
page_to_pfn(subpage));
if (pte_young(pteval))
entry = make_migration_entry_young(entry);
if (pte_dirty(pteval))
entry = make_migration_entry_dirty(entry);
swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_uffd_wp(pteval))
swp_pte = pte_swp_mkuffd_wp(swp_pte);
if (likely(pte_present(pteval))) {
if (pte_young(pteval))
entry = make_migration_entry_young(entry);
if (pte_dirty(pteval))
entry = make_migration_entry_dirty(entry);
swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_uffd_wp(pteval))
swp_pte = pte_swp_mkuffd_wp(swp_pte);
} else {
swp_pte = swp_entry_to_pte(entry);
if (pte_swp_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_swp_uffd_wp(pteval))
swp_pte = pte_swp_mkuffd_wp(swp_pte);
}
if (folio_test_hugetlb(folio))
set_huge_pte_at(mm, address, pvmw.pte, swp_pte,
hsz);