Jann reported a race between munmap() and unmap_mapping_range(), where
unmap_mapping_range() will no-op once unmap_vmas() has unlinked the
VMA; however munmap() will not yet have invalidated the TLBs.
Therefore unmap_mapping_range() will complete while there are still
(stale) TLB entries for the specified range.
Mitigate this by force flushing TLBs for VM_PFNMAP ranges.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
include/asm-generic/tlb.h | 33 +++++++++++++++++----------------
1 file changed, 17 insertions(+), 16 deletions(-)
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -303,6 +303,7 @@ struct mmu_gather {
*/
unsigned int vma_exec : 1;
unsigned int vma_huge : 1;
+ unsigned int vma_pfn : 1;
unsigned int batch_count;
@@ -373,7 +374,6 @@ tlb_update_vma_flags(struct mmu_gather *
#else /* CONFIG_MMU_GATHER_NO_RANGE */
#ifndef tlb_flush
-
/*
* When an architecture does not provide its own tlb_flush() implementation
* but does have a reasonably efficient flush_vma_range() implementation
@@ -393,6 +393,9 @@ static inline void tlb_flush(struct mmu_
flush_tlb_range(&vma, tlb->start, tlb->end);
}
}
+#endif
+
+#endif /* CONFIG_MMU_GATHER_NO_RANGE */
static inline void
tlb_update_vma_flags(struct mmu_gather *tlb, struct vm_area_struct *vma)
@@ -410,17 +413,9 @@ tlb_update_vma_flags(struct mmu_gather *
*/
tlb->vma_huge = is_vm_hugetlb_page(vma);
tlb->vma_exec = !!(vma->vm_flags & VM_EXEC);
+ tlb->vma_pfn = !!(vma->vm_flags & VM_PFNMAP);
}
-#else
-
-static inline void
-tlb_update_vma_flags(struct mmu_gather *tlb, struct vm_area_struct *vma) { }
-
-#endif
-
-#endif /* CONFIG_MMU_GATHER_NO_RANGE */
-
static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
{
/*
@@ -507,16 +502,22 @@ static inline void tlb_start_vma(struct
static inline void tlb_end_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
{
- if (tlb->fullmm || IS_ENABLED(CONFIG_MMU_GATHER_MERGE_VMAS))
+ if (tlb->fullmm)
return;
/*
- * Do a TLB flush and reset the range at VMA boundaries; this avoids
- * the ranges growing with the unused space between consecutive VMAs,
- * but also the mmu_gather::vma_* flags from tlb_start_vma() rely on
- * this.
+ * 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.
*/
- tlb_flush_mmu_tlbonly(tlb);
+ 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);
+ }
}
/*
