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b=Lfka2xABH4WlCH4+Kcss1VPXGMllQT4xshc3EanCjCi2KvTd4/QdGhadS1atYJxN9 4QkETM0uJkIzS9CERgnRpjWb0kDTrRBCffxgEc9S+X4SoqsI6SLDXzW+/JyjPofaJm TzK/U7C0PBQwZKaToMx+Vqy0eEdZ0iAeNKWhQHStqLyYV7eGzhVXikwfiMCSJCs7xR Qiqp57S5pu7nnGzKbPyFYU/5kcXyA2Sr1GQWZC61FlnjjkdAtXq1aGCfXkVIg8Z01x un+M6OSbEtVRK4P3KbjkTPPG7d2HH/Y9pcfvKMBzmS/vt7xX+4XWEdfBKQBH31mfEy Uwj5mmyWpXBbA== Message-ID: <2252683e-df5d-47ce-b15d-1036bef8d063@kernel.org> Date: Thu, 25 Jun 2026 12:37:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Patch mm-hotfixes v4] mm/page_vma_mapped: fix device-private PMD handling To: Wei Yang , Lance Yang Cc: akpm@linux-foundation.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, ziy@nvidia.com, sj@kernel.org, balbirs@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260624065353.1622-1-richard.weiyang@gmail.com> <20260624085756.6598-1-lance.yang@linux.dev> <20260625095728.woikmkxb6gskth3b@master> 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-Rspam-User: X-Stat-Signature: g9reecj9kz6jkm9cjcnucegoi1bf3euq X-Rspamd-Queue-Id: 0FFD420003 X-Rspamd-Server: rspam06 X-HE-Tag: 1782383881-628408 X-HE-Meta: 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 3+3N/ngf 9jJlbsPPrM/DKTMWNUNpf/F2o3CFLn4nkdhnh73C7ArwIp6CdCYSd69XKwtbFbBx8DX5jlnmGOz3UA29f/yqI6FOMp0QxTvrmEemA8riDlv9LE38Evx0a9vCHcM9owarjW0rZVbolPUcl79TTN0+V1Oa1xaIrdI4x3YUeJ7FD14PWB8OQQjAQKr9MQ5gyeU3MWzHQ+WbgSCKAgmywBMq1KmJLp3CTZwKRka8vmGhbOT1ZFDx1i8PM9T1TYUiC3OPFjyUgEGnJL1296axC5tpa7wNPlYkz3d6vJbc1zybx4kz64rupRQxKRufl2eZLYti1nZIuucq2EqoNqeilEirp3cVBHgnie6M5B3yt3k49UguSA3X+yyPofUenx+UA8yx5vd2eBCkstUJUJy0rPPZiqucZbA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> CPU0: pmde = pmdp_get_lockless(); // sees PMD migration entry >> >> CPU1: remove_migration_ptes(src, dst /* device-private */) >> ... via rmap_walk(dst) ... >> page_vma_mapped_walk(&pvmw /* src, PVMW_MIGRATION */) >> returns with PTL held for the PMD migration entry >> remove_migration_pmd(new = dst page) >> installs a device-private PMD >> next page_vma_mapped_walk() >> drops PTL via not_found() >> >> CPU0: takes PTL >> pmde = *pvmw->pmd; // now device-private PMD >> >> So when PVMW_MIGRATION is not set, current code can return not_found() >> before we even decode the locked PMD as a device-private entry. >> >> Commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration support >> device-private entries") made the >> >> device-private PMD <-> PMD migration >> >> transition possible. Doesn't the folio lock help here already? -- Cheers, David