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[2003:cb:c707:c500:5445:cf40:2e32:6e73]) by smtp.gmail.com with ESMTPSA id v5-20020a1cac05000000b003a626055569sm1122379wme.16.2022.08.24.01.21.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Aug 2022 01:21:55 -0700 (PDT) Message-ID: <86b0622d-06eb-cfab-2ff1-8a0eaf823f8a@redhat.com> Date: Wed, 24 Aug 2022 10:21:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH v3 1/3] mm/migrate_device.c: Flush TLB while holding PTL Content-Language: en-US To: Alistair Popple , linux-mm@kvack.org, akpm@linux-foundation.org Cc: Peter Xu , Nadav Amit , huang ying , LKML , "Sierra Guiza, Alejandro (Alex)" , Felix Kuehling , Jason Gunthorpe , John Hubbard , Ralph Campbell , Matthew Wilcox , Karol Herbst , Lyude Paul , Ben Skeggs , Logan Gunthorpe , paulus@ozlabs.org, linuxppc-dev@lists.ozlabs.org, stable@vger.kernel.org References: <3b01af093515ce2960ac39bb16ff77473150d179.1661309831.git-series.apopple@nvidia.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <3b01af093515ce2960ac39bb16ff77473150d179.1661309831.git-series.apopple@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24.08.22 05:03, 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 > Reported-by: Nadav Amit > Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") > Cc: stable@vger.kernel.org > > --- > > 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 I'm not a TLB-flushing expert, but this matches my understanding (and a TLB flushing Linux documentation I stumbled over some while ago but cannot quickly find). In the ordinary try_to_migrate_one() path, flushing would happen via ptep_clear_flush() (just like we do for the anon_exclusive case here as well), correct? -- Thanks, David / dhildenb