Ever since commit b756a3b5e7ea ("mm: device exclusive memory access")
we can return with a device-exclusive entry from page_vma_mapped_walk().
try_to_unmap_one() is not prepared for that, so teach it about these
PFN swap PTEs. Note that device-private entries are so far not
applicable on that path, as we expect ZONE_DEVICE pages so far only in
migration code when it comes to the RMAP.
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_unmap() calls MMU notifiers and holds the
folio lock, so any device-exclusive users should be properly prepared
for a device-exclusive PTE to "vanish".
Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/rmap.c | 52 +++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 39 insertions(+), 13 deletions(-)
diff --git a/mm/rmap.c b/mm/rmap.c
index 1129ed132af94..47142a656ae51 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1648,9 +1648,9 @@ static bool try_to_unmap_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, 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;
@@ -1722,7 +1722,18 @@ static bool try_to_unmap_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));
+ /*
+ * 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 {
+ 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) &&
@@ -1778,7 +1789,9 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
hugetlb_vma_unlock_write(vma);
}
pteval = huge_ptep_clear_flush(vma, address, pvmw.pte);
- } else {
+ if (pte_dirty(pteval))
+ folio_mark_dirty(folio);
+ } else if (likely(pte_present(pteval))) {
flush_cache_page(vma, address, pfn);
/* Nuke the page table entry. */
if (should_defer_flush(mm, flags)) {
@@ -1796,6 +1809,10 @@ static bool try_to_unmap_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);
+ } else {
+ pte_clear(mm, address, pvmw.pte);
}
/*
@@ -1805,10 +1822,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
*/
pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pteval);
- /* Set the dirty flag on the folio now the pte is gone. */
- if (pte_dirty(pteval))
- folio_mark_dirty(folio);
-
/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
@@ -1822,8 +1835,8 @@ static bool try_to_unmap_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
@@ -1902,6 +1915,12 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
set_pte_at(mm, address, pvmw.pte, pteval);
goto walk_abort;
}
+
+ /*
+ * 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) {
swap_free(entry);
set_pte_at(mm, address, pvmw.pte, pteval);
@@ -1926,10 +1945,17 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
swp_pte = swp_entry_to_pte(entry);
if (anon_exclusive)
swp_pte = pte_swp_mkexclusive(swp_pte);
- 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_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 {
+ 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, address, pvmw.pte, swp_pte);
} else {
/*
--
2.48.1
