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Date: Fri, 2 Sep 2022 08:51:53 +0200 From: David Hildenbrand <david@...hat.com> To: Alistair Popple <apopple@...dia.com>, linux-mm@...ck.org, akpm@...ux-foundation.org Cc: Peter Xu <peterx@...hat.com>, Nadav Amit <nadav.amit@...il.com>, huang ying <huang.ying.caritas@...il.com>, LKML <linux-kernel@...r.kernel.org>, "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>, Felix Kuehling <Felix.Kuehling@....com>, Jason Gunthorpe <jgg@...dia.com>, John Hubbard <jhubbard@...dia.com>, Ralph Campbell <rcampbell@...dia.com>, Matthew Wilcox <willy@...radead.org>, Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>, Ben Skeggs <bskeggs@...hat.com>, Logan Gunthorpe <logang@...tatee.com>, paulus@...abs.org, linuxppc-dev@...ts.ozlabs.org, "Huang, Ying" <ying.huang@...el.com>, stable@...r.kernel.org Subject: Re: [PATCH v4 1/4] mm/migrate_device.c: Flush TLB while holding PTL On 02.09.22 02:35, Alistair Popple wrote: > When clearing a PTE the TLB should be flushed whilst still holding the > PTL to avoid a potential race with madvise/munmap/etc. For example > consider the following sequence: > > CPU0 CPU1 > ---- ---- > > migrate_vma_collect_pmd() > pte_unmap_unlock() > madvise(MADV_DONTNEED) > -> zap_pte_range() > pte_offset_map_lock() > [ PTE not present, TLB not flushed ] > pte_unmap_unlock() > [ page is still accessible via stale TLB ] > flush_tlb_range() > > In this case the page may still be accessed via the stale TLB entry > after madvise returns. Fix this by flushing the TLB while holding the > PTL. > > Signed-off-by: Alistair Popple <apopple@...dia.com> > Reported-by: Nadav Amit <nadav.amit@...il.com> > Reviewed-by: "Huang, Ying" <ying.huang@...el.com> > Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") > Cc: stable@...r.kernel.org > > --- > > Changes for v4: > > - Added Review-by > > Changes for v3: > > - New for v3 > --- > mm/migrate_device.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 27fb37d..6a5ef9f 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -254,13 +254,14 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > migrate->dst[migrate->npages] = 0; > migrate->src[migrate->npages++] = mpfn; > } > - arch_leave_lazy_mmu_mode(); > - pte_unmap_unlock(ptep - 1, ptl); > > /* Only flush the TLB if we actually modified any entries */ > if (unmapped) > flush_tlb_range(walk->vma, start, end); > > + arch_leave_lazy_mmu_mode(); > + pte_unmap_unlock(ptep - 1, ptl); > + > return 0; > } > > > base-commit: ffcf9c5700e49c0aee42dcba9a12ba21338e8136 Acked-by: David Hildenbrand <david@...hat.com> -- Thanks, David / dhildenb
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