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a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784200905; bh=jW9Bml3oYmUGAOmKPLAJ2CnP/L0HuV5RHmyp2e90SIc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=htqNAfT2yuc/+HqsQQgqkOeo3B5rAr9UM8Ovms/+FzWEnHs1gXx60lGZ5KC9gpnlK L+/KxPrqScYi6x81ENHVw9cNphhIEtcljCFw7EVh4iMPP1SotWfLCPN2x9ZEVtEqXO IdI+XGELqaL7cQi9Vx2HBT7cDSBgFG3FtFNpQmjIKMFfibqvfkaQxj7q1QaB9zprkb DSYyJZinKVHCOjjDPAMaG4HgW/XaHJkyMW9tMklhv5IbEr/AtslVVoZCi30NCdAs/x EZcK0B5LpQBC4SESt8DUUbjeBCsw9onw8x6EAYSEgHQOIYaOpZsPJayKJUcO9qG4Dl xEpoIyuE/NGiw== Message-ID: Date: Thu, 16 Jul 2026 13:21:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 1/2] fs/proc/task_mmu: fix PAGEMAP_SCAN written state for PMD holes To: Kiryl Shutsemau , akpm@linux-foundation.org Cc: usama.anjum@arm.com, peterx@redhat.com, liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, rppt@kernel.org, surenb@google.com, mhocko@suse.com, zenghui.yu@linux.dev, shuah@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org, kernel-team@meta.com References: <20260715144234.442721-1-kirill@shutemov.name> <20260715144234.442721-2-kirill@shutemov.name> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: EEF9F4000B X-Rspam-User: X-Stat-Signature: uwdk56hrm87ijabwrjf9397s7o8b1hpm X-Rspamd-Server: rspam03 X-HE-Tag: 1784200907-651825 X-HE-Meta: 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 kdpiGYaM kI/orPUWWw971YDV4d9cWSKdtUZwpEoAiFLTrmSDJrkaKhBlpGydZJm1yWMPOOj1lZiCSXVAqpN8NiRNbFOY3N0htU0AD+fnp20jGPg9CyhQuFDdoboNGxY11/OX1pj7JJKLJHsVSpnimeXVERzSvVvRf6lx1HrfL792kgTKEVFB8/T25O92q4Z+4KrSynN4BtkLuLTspFKsNKSd3Q23XDiQktd3/kmw+CTcnTpUiPjDxXYtawm/3qP4PoKVPBKqtMQ53x5rSVSxpGf8JwQEXuRl4QtLve3aoV4TudtmfpPk2m56JXcwUDYGmD+rp38/UJYdZlG4BAIE73drGnSjPswTw8Cf55nOidAEyngVt32ld2k1iXDYw0D2DSu4vrNq/9MAc//yhmvCR+kMLqZuSWuXwdTS9MAqT16H5DLA0r2VhdLSrHXKX+t6K1kFDmc06CVH82TOzyHvaPT5rlf8RTTC3+w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/15/26 16:42, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > PAGEMAP_SCAN reports an unpopulated PTE in a uffd-wp VMA as written, but > a range with no page table at all -- a PMD hole -- is skipped: > pagemap_scan_pte_hole() tests p->cur_vma_category, which never carries > PAGE_IS_WRITTEN, so the hole is neither reported nor (under > PM_SCAN_WP_MATCHING) armed. > > In a uffd-wp VMA, WP_UNPOPULATED installs uffd-wp markers when protecting > a range, allocating page tables as needed, so an unpopulated slot is > treated as written -- see the pte_none() handling in > pagemap_page_category(). A missing marker therefore means the range was > zapped, e.g. via MADV_DONTNEED. This applies to anon and shmem VMAs. > > An anonymous THP is write-protected in place as a huge PMD, so a > full-PMD MADV_DONTNEED clears it to pmd_none -- a hole with no page table > -- and pagemap_scan_pte_hole() misses it. For a MAP_PRIVATE|MAP_ANON > mapping MADV_DONTNEED has fill-with-zeros semantics, so a write-tracking > checkpoint/migration tool (e.g. CRIU) treats the range as unchanged and > keeps its previous contents; after restore or live migration the process > reads stale data instead of zeroes -- data corruption. > > Report a hole in a non-hugetlb uffd-wp VMA as written, matching the > pte_none handling in pagemap_page_category(); the existing > PM_SCAN_WP_MATCHING path then arms it via uffd_wp_range(). > > hugetlb is excluded: pagemap_hugetlb_category() reports an empty hugetlb > entry (huge_pte_none) as not-written, unlike pagemap_page_category(), > which reports pte_none as written. pagemap_scan_pte_hole() fires for a > hugetlb slot only when it has no page table; keeping that not-written > matches how an allocated-but-empty hugetlb entry reads, so the hole and > the empty-entry cases agree within the VMA. > > Reported-by: Sashiko AI review > Closes: https://sashiko.dev/#/patchset/20260707151349.92143-1-kirill@shutemov.name > Fixes: 2bad466cc9d9 ("mm/uffd: UFFD_FEATURE_WP_UNPOPULATED") > Cc: Muhammad Usama Anjum > Cc: Peter Xu > Cc: stable@vger.kernel.org > Signed-off-by: Kiryl Shutsemau > Assisted-by: Claude:claude-fable-5 > --- Thanks! Acked-by: David Hildenbrand (Arm) -- Cheers, David