Commit b67fbebd4cf9 ("mmu_gather: Force tlb-flush VM_PFNMAP vmas")
added a forced tlbflush to tlb_vma_end(), which is required to avoid a
race between munmap() and unmap_mapping_range(). However it added some
overhead to other paths where tlb_vma_end() is used, but vmas are not
removed, e.g. madvise(MADV_DONTNEED).
Fix this by moving the tlb flush out of tlb_end_vma() into
free_pgtables(), somewhat similar to the stable version of the
original commit: e.g. stable commit 895428ee124a ("mm: Force TLB flush
for PFNMAP mappings before unlink_file_vma()").
Note, that if tlb->fullmm is set, no flush is required, as the whole
mm is about to be destroyed.
---
v3:
- added initialization of vma_pfn in __tlb_reset_range() (by Hugh D.)
v2:
- moved vma_pfn flag handling into tlb.h (by Peter Z.)
- added comments (by Peter Z.)
- fixed the vma_pfn flag setting (by Hugh D.)
Suggested-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
include/asm-generic/tlb.h | 49 ++++++++++++++++++++++++++++-----------
mm/memory.c | 7 ++++++
2 files changed, 42 insertions(+), 14 deletions(-)
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 709830274b75..cdc95b69b91d 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -380,8 +380,16 @@ static inline void __tlb_reset_range(struct mmu_gather *tlb)
tlb->cleared_pmds = 0;
tlb->cleared_puds = 0;
tlb->cleared_p4ds = 0;
+
+ /*
+ * vma_pfn can only be set in tlb_start_vma(), so let's
+ * initialize it here. Also a tlb flush issued by
+ * tlb_flush_mmu_pfnmap() will cancel the vma_pfn state,
+ * so that unnecessary subsequent flushes are avoided.
+ */
+ tlb->vma_pfn = 0;
/*
- * Do not reset mmu_gather::vma_* fields here, we do not
+ * Do not reset other mmu_gather::vma_* fields here, we do not
* call into tlb_start_vma() again to set them if there is an
* intermediate flush.
*/
@@ -449,7 +457,14 @@ tlb_update_vma_flags(struct mmu_gather *tlb, struct vm_area_struct *vma)
*/
tlb->vma_huge = is_vm_hugetlb_page(vma);
tlb->vma_exec = !!(vma->vm_flags & VM_EXEC);
- tlb->vma_pfn = !!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP));
+
+ /*
+ * vma_pfn is checked and cleared by tlb_flush_mmu_pfnmap()
+ * for a set of vma's, so it should be set if at least one vma
+ * has VM_PFNMAP or VM_MIXEDMAP flags set.
+ */
+ if (vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))
+ tlb->vma_pfn = 1;
}
static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
@@ -466,6 +481,20 @@ static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
__tlb_reset_range(tlb);
}
+static inline void tlb_flush_mmu_pfnmap(struct mmu_gather *tlb)
+{
+ /*
+ * VM_PFNMAP and VM_MIXEDMAP maps are fragile because the core mm
+ * doesn't track the page mapcount -- there might not be page-frames
+ * for these PFNs after all. Force flush TLBs for such ranges to avoid
+ * munmap() vs unmap_mapping_range() races.
+ * Ensure we have no stale TLB entries by the time this mapping is
+ * removed from the rmap.
+ */
+ if (unlikely(!tlb->fullmm && tlb->vma_pfn))
+ tlb_flush_mmu_tlbonly(tlb);
+}
+
static inline void tlb_remove_page_size(struct mmu_gather *tlb,
struct page *page, int page_size)
{
@@ -549,22 +578,14 @@ static inline void tlb_start_vma(struct mmu_gather *tlb, struct vm_area_struct *
static inline void tlb_end_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
{
- if (tlb->fullmm)
+ if (tlb->fullmm || IS_ENABLED(CONFIG_MMU_GATHER_MERGE_VMAS))
return;
/*
- * VM_PFNMAP is more fragile because the core mm will not track the
- * page mapcount -- there might not be page-frames for these PFNs after
- * all. Force flush TLBs for such ranges to avoid munmap() vs
- * unmap_mapping_range() races.
+ * Do a TLB flush and reset the range at VMA boundaries; this avoids
+ * the ranges growing with the unused space between consecutive VMAs.
*/
- if (tlb->vma_pfn || !IS_ENABLED(CONFIG_MMU_GATHER_MERGE_VMAS)) {
- /*
- * Do a TLB flush and reset the range at VMA boundaries; this avoids
- * the ranges growing with the unused space between consecutive VMAs.
- */
- tlb_flush_mmu_tlbonly(tlb);
- }
+ tlb_flush_mmu_tlbonly(tlb);
}
/*
diff --git a/mm/memory.c b/mm/memory.c
index 398c031be9ba..c2a9effb2e32 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -365,6 +365,13 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
{
struct unlink_vma_file_batch vb;
+ /*
+ * VM_PFNMAP and VM_MIXEDMAP maps require a special handling here:
+ * force flush TLBs for such ranges to avoid munmap() vs
+ * unmap_mapping_range() races.
+ */
+ tlb_flush_mmu_pfnmap(tlb);
+
do {
unsigned long addr = vma->vm_start;
struct vm_area_struct *next;
--
2.48.1.262.g85cc9f2d1e-goog
