Some of the features (unmap, migrate, device exclusive, mkclean, etc)
might modify the pte entry via rmap. Add a new page vma mapped walk
flag, PVMW_BREAK_COW_PTE, to indicate the rmap walking to break COW PTE.
Signed-off-by: Chih-En Lin <shiyn.lin@xxxxxxxxx>
---
include/linux/rmap.h | 2 ++
mm/migrate.c | 3 ++-
mm/page_vma_mapped.c | 2 ++
mm/rmap.c | 12 +++++++-----
mm/vmscan.c | 7 ++++++-
5 files changed, 19 insertions(+), 7 deletions(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index bd3504d11b155..d0f07e5519736 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -368,6 +368,8 @@ int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
#define PVMW_SYNC (1 << 0)
/* Look for migration entries rather than present PTEs */
#define PVMW_MIGRATION (1 << 1)
+/* Break COW-ed PTE during walking */
+#define PVMW_BREAK_COW_PTE (1 << 2)
struct page_vma_mapped_walk {
unsigned long pfn;
diff --git a/mm/migrate.c b/mm/migrate.c
index dff333593a8ae..a4be7e04c9b09 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -174,7 +174,8 @@ void putback_movable_pages(struct list_head *l)
static bool remove_migration_pte(struct folio *folio,
struct vm_area_struct *vma, unsigned long addr, void *old)
{
- DEFINE_FOLIO_VMA_WALK(pvmw, old, vma, addr, PVMW_SYNC | PVMW_MIGRATION);
+ DEFINE_FOLIO_VMA_WALK(pvmw, old, vma, addr,
+ PVMW_SYNC | PVMW_MIGRATION | PVMW_BREAK_COW_PTE);
while (page_vma_mapped_walk(&pvmw)) {
rmap_t rmap_flags = RMAP_NONE;
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 93e13fc17d3cb..5dfc9236dc505 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -251,6 +251,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
step_forward(pvmw, PMD_SIZE);
continue;
}
+ if (pvmw->flags & PVMW_BREAK_COW_PTE)
+ break_cow_pte(vma, pvmw->pmd, pvmw->address);
if (!map_pte(pvmw))
goto next_pte;
this_pte:
diff --git a/mm/rmap.c b/mm/rmap.c
index 2ec925e5fa6a9..b1b7dcbd498be 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -807,7 +807,8 @@ static bool folio_referenced_one(struct folio *folio,
struct vm_area_struct *vma, unsigned long address, void *arg)
{
struct folio_referenced_arg *pra = arg;
- DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
+ /* it will clear the entry, so we should break COW PTE. */
+ DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_BREAK_COW_PTE);
int referenced = 0;
while (page_vma_mapped_walk(&pvmw)) {
@@ -1012,7 +1013,8 @@ static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
static bool page_mkclean_one(struct folio *folio, struct vm_area_struct *vma,
unsigned long address, void *arg)
{
- DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_SYNC);
+ DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address,
+ PVMW_SYNC | PVMW_BREAK_COW_PTE);
int *cleaned = arg;
*cleaned += page_vma_mkclean_one(&pvmw);
@@ -1471,7 +1473,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
unsigned long address, void *arg)
{
struct mm_struct *mm = vma->vm_mm;
- DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
+ DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_BREAK_COW_PTE);
pte_t pteval;
struct page *subpage;
bool anon_exclusive, ret = true;
@@ -1842,7 +1844,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
unsigned long address, void *arg)
{
struct mm_struct *mm = vma->vm_mm;
- DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
+ DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_BREAK_COW_PTE);
pte_t pteval;
struct page *subpage;
bool anon_exclusive, ret = true;
@@ -2195,7 +2197,7 @@ static bool page_make_device_exclusive_one(struct folio *folio,
struct vm_area_struct *vma, unsigned long address, void *priv)
{
struct mm_struct *mm = vma->vm_mm;
- DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
+ DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_BREAK_COW_PTE);
struct make_exclusive_args *args = priv;
pte_t pteval;
struct page *subpage;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 026199c047e0e..980d2056adfd1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1781,6 +1781,10 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
}
}
+ /*
+ * Break COW PTE since checking the reference
+ * of folio might modify the PTE.
+ */
if (!ignore_references)
references = folio_check_references(folio, sc);
@@ -1864,7 +1868,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
/*
* The folio is mapped into the page tables of one or more
- * processes. Try to unmap it here.
+ * processes. Try to unmap it here. Also, since it will write
+ * to the page tables, break COW PTE if they are.
*/
if (folio_mapped(folio)) {
enum ttu_flags flags = TTU_BATCH_FLUSH;
--
2.37.3
