| Message ID | 20220708071834.149930530@infradead.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | munmap() vs unmap_mapping_range() | expand |
On Fri, Jul 08, 2022 at 09:18:06AM +0200, Peter Zijlstra wrote: > 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@infradead.org> > --- > 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); > + } We already have the vma here, so I'm not sure how much the new 'vma_pfn' field really buys us over checking the 'vm_flags', but perhaps that's cleanup for another day. Acked-by: Will Deacon <will@kernel.org> Will
On Fri, Jul 08, 2022 at 02:36:06PM +0100, Will Deacon wrote: > On Fri, Jul 08, 2022 at 09:18:06AM +0200, Peter Zijlstra wrote: > > @@ -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); > > + } > > We already have the vma here, so I'm not sure how much the new 'vma_pfn' > field really buys us over checking the 'vm_flags', but perhaps that's > cleanup for another day. Duh, that's just me being daft again. For some raisin I was convinced (and failed to check) that we only had the vma at start. I can easily respin this to not need the extra variable. How's this then? --- Subject: mmu_gather: Force tlb-flush VM_PFNMAP vmas From: Peter Zijlstra <peterz@infradead.org> Date: Thu Jul 7 11:51:16 CEST 2022 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@infradead.org> --- include/asm-generic/tlb.h | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -507,16 +507,22 @@ 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 ((vma->vm_flags & VM_PFNMAP) || !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); + } } /*
On Fri, Jul 8, 2022 at 9:19 AM Peter Zijlstra <peterz@infradead.org> wrote: > 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@infradead.org> > --- > 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); We should probably handle VM_MIXEDMAP the same way as VM_PFNMAP here, I think? Conceptually I think the same issue can happen with device-owned pages that aren't managed by the kernel's page allocator, and for those, VM_MIXEDMAP is the same as 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; Is this correct, or would there still be a race between MM teardown (which sets ->fullmm, see exit_mmap()->tlb_gather_mmu_fullmm()) and unmap_mapping_range()? My understanding is that ->fullmm only guarantees a flush at tlb_finish_mmu(), but here we're trying to ensure a flush before unlink_file_vma(). > /* > - * 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. Maybe add: "We do *not* guarantee that after munmap() has passed through tlb_end_vma(), there are no more stale TLB entries for this VMA; there could be a parallel PTE-zapping operation that has zapped PTEs before we looked at them but hasn't done the corresponding TLB flush yet. However, such a parallel zap can't be done through the mm_struct (we've unlinked the VMA), so it would have to be done under the ->i_mmap_sem in read mode, which we synchronize against in unlink_file_vma()." I'm not convinced it's particularly nice to do a flush in tlb_end_vma() when we can't make guarantees about the TLB state wrt parallel invalidations, and when we only really care about having a flush between unmap_vmas() and free_pgtables(), but I guess it works? > */ > - 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); > + } > } > > /* > >
On Fri, Jul 08, 2022 at 04:04:38PM +0200, Jann Horn wrote: > On Fri, Jul 8, 2022 at 9:19 AM Peter Zijlstra <peterz@infradead.org> wrote: > > 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@infradead.org> > > --- > > 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); > > We should probably handle VM_MIXEDMAP the same way as VM_PFNMAP here, > I think? Conceptually I think the same issue can happen with > device-owned pages that aren't managed by the kernel's page allocator, > and for those, VM_MIXEDMAP is the same as VM_PFNMAP. Hmm, yeah, that seems to make sense. > > } > > > > -#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; > > Is this correct, or would there still be a race between MM teardown > (which sets ->fullmm, see exit_mmap()->tlb_gather_mmu_fullmm()) and > unmap_mapping_range()? My understanding is that ->fullmm only > guarantees a flush at tlb_finish_mmu(), but here we're trying to > ensure a flush before unlink_file_vma(). fullmm is when the last user of the mm goes away, there should not be any races on the address space at that time. Also see the comment with tlb_gather_mmu_fullmm() and its users. > > /* > > - * 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. > > Maybe add: "We do *not* guarantee that after munmap() has passed ^ otherwise? > through tlb_end_vma(), there are no more stale TLB entries for this > VMA; there could be a parallel PTE-zapping operation that has zapped > PTEs before we looked at them but hasn't done the corresponding TLB > flush yet. However, such a parallel zap can't be done through the > mm_struct (we've unlinked the VMA), so it would have to be done under > the ->i_mmap_sem in read mode, which we synchronize against in > unlink_file_vma()." Done. > I'm not convinced it's particularly nice to do a flush in > tlb_end_vma() when we can't make guarantees about the TLB state wrt > parallel invalidations, and when we only really care about having a > flush between unmap_vmas() and free_pgtables(), but I guess it works? Yeah, none of this is pretty. I despise this whole parallel invalidation stuff with a passion, we've had ever so many bugs because of that :-( We could add another mmu_gather callback and place it between unmap_vmas() and free_pgtables(), but it's a much larger patch and I'm not entirely sure it's worth the complexity. OTOH having a callback between freeing pages and freeing page-tables might not be the worst idea. Let me ponder that for a bit. Meanwhile; updated patch below. --- Subject: mmu_gather: Force TLB-flush VM_PFNMAP|VM_MIXEDMAP vmas From: Peter Zijlstra <peterz@infradead.org> Date: Thu Jul 7 11:51:16 CEST 2022 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. Reported-by: Jann Horn <jannh@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- include/asm-generic/tlb.h | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -507,16 +507,32 @@ 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|VM_MIXEDMAP 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. + * + * We do *NOT* guarantee that after munmap() has passed through + * tlb_end_vma(), there are no more stale TLB entries for this VMA; + * there could be a parallel PTE-zapping operation that has zapped PTEs + * before we looked at them but hasn't done the corresponding TLB flush + * yet. However, such a parallel zap can't be done through the + * mm_struct (we've unliked the VMA), so it would have to be done under + * the ->i_mmap_sem in read move, which we synchronize against in + * unlink_file_vma(). */ - tlb_flush_mmu_tlbonly(tlb); + if ((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) || + !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); + } } /*
On Sat, Jul 9, 2022 at 10:38 AM Peter Zijlstra <peterz@infradead.org> wrote: > On Fri, Jul 08, 2022 at 04:04:38PM +0200, Jann Horn wrote: > > On Fri, Jul 8, 2022 at 9:19 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > @@ -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; > > > > Is this correct, or would there still be a race between MM teardown > > (which sets ->fullmm, see exit_mmap()->tlb_gather_mmu_fullmm()) and > > unmap_mapping_range()? My understanding is that ->fullmm only > > guarantees a flush at tlb_finish_mmu(), but here we're trying to > > ensure a flush before unlink_file_vma(). > > fullmm is when the last user of the mm goes away, there should not be (FWIW, there also seems to be an error path in write_ldt -> free_ldt_pgtables -> tlb_gather_mmu_fullmm where ->fullmm can be set for a TLB shootdown in a live process, but that's irrelevant for this patch.) > any races on the address space at that time. Also see the comment with > tlb_gather_mmu_fullmm() and its users. Ah, right, aside from the LDT weirdness, fullmm is only used in exit_mmap, and at that point there can be no more parallel access to the MM except for remote memory reaping (which is synchronized against using mmap_write_lock()) and rmap walks... > Subject: mmu_gather: Force TLB-flush VM_PFNMAP|VM_MIXEDMAP vmas > From: Peter Zijlstra <peterz@infradead.org> > Date: Thu Jul 7 11:51:16 CEST 2022 > > 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. > > Reported-by: Jann Horn <jannh@google.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Looks good to me.
--- 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); + } } /*
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@infradead.org> --- include/asm-generic/tlb.h | 33 +++++++++++++++++---------------- 1 file changed, 17 insertions(+), 16 deletions(-)