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Subject[PATCH 4/6] mm: proc: Invalidate TLB after clearing soft-dirty page state
Date
Since commit 0758cd830494 ("asm-generic/tlb: avoid potential double flush"),
TLB invalidation is elided in tlb_finish_mmu() if no entries were batched
via the tlb_remove_*() functions. Consequently, the page-table modifications
performed by clear_refs_write() in response to a write to
/proc/<pid>/clear_refs do not perform TLB invalidation. Although this is
fine when simply aging the ptes, in the case of clearing the "soft-dirty"
state we can end up with entries where pte_write() is false, yet a
writable mapping remains in the TLB.

Fix this by calling tlb_remove_tlb_entry() for each entry being
write-protected when cleating soft-dirty.

Signed-off-by: Will Deacon <will@kernel.org>
---
fs/proc/task_mmu.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index cd03ab9087b0..3308292ee5c5 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1032,11 +1032,12 @@ enum clear_refs_types {

struct clear_refs_private {
enum clear_refs_types type;
+ struct mmu_gather *tlb;
};

#ifdef CONFIG_MEM_SOFT_DIRTY
static inline void clear_soft_dirty(struct vm_area_struct *vma,
- unsigned long addr, pte_t *pte)
+ unsigned long addr, pte_t *pte, struct mmu_gather *tlb)
{
/*
* The soft-dirty tracker uses #PF-s to catch writes
@@ -1053,6 +1054,7 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
ptent = pte_wrprotect(old_pte);
ptent = pte_clear_soft_dirty(ptent);
ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent);
+ tlb_remove_tlb_entry(tlb, pte, addr);
} else if (is_swap_pte(ptent)) {
ptent = pte_swp_clear_soft_dirty(ptent);
set_pte_at(vma->vm_mm, addr, pte, ptent);
@@ -1060,14 +1062,14 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
}
#else
static inline void clear_soft_dirty(struct vm_area_struct *vma,
- unsigned long addr, pte_t *pte)
+ unsigned long addr, pte_t *pte, struct mmu_gather *tlb)
{
}
#endif

#if defined(CONFIG_MEM_SOFT_DIRTY) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,
- unsigned long addr, pmd_t *pmdp)
+ unsigned long addr, pmd_t *pmdp, struct mmu_gather *tlb)
{
pmd_t old, pmd = *pmdp;

@@ -1081,6 +1083,7 @@ static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,

pmd = pmd_wrprotect(pmd);
pmd = pmd_clear_soft_dirty(pmd);
+ tlb_remove_pmd_tlb_entry(tlb, pmdp, addr);

set_pmd_at(vma->vm_mm, addr, pmdp, pmd);
} else if (is_migration_entry(pmd_to_swp_entry(pmd))) {
@@ -1090,7 +1093,7 @@ static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,
}
#else
static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,
- unsigned long addr, pmd_t *pmdp)
+ unsigned long addr, pmd_t *pmdp, struct mmu_gather *tlb)
{
}
#endif
@@ -1107,7 +1110,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
ptl = pmd_trans_huge_lock(pmd, vma);
if (ptl) {
if (cp->type == CLEAR_REFS_SOFT_DIRTY) {
- clear_soft_dirty_pmd(vma, addr, pmd);
+ clear_soft_dirty_pmd(vma, addr, pmd, cp->tlb);
goto out;
}

@@ -1133,7 +1136,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
ptent = *pte;

if (cp->type == CLEAR_REFS_SOFT_DIRTY) {
- clear_soft_dirty(vma, addr, pte);
+ clear_soft_dirty(vma, addr, pte, cp->tlb);
continue;
}

@@ -1212,7 +1215,8 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
if (mm) {
struct mmu_notifier_range range;
struct clear_refs_private cp = {
- .type = type,
+ .type = type,
+ .tlb = &tlb,
};

if (type == CLEAR_REFS_MM_HIWATER_RSS) {
--
2.29.2.454.gaff20da3a2-goog
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