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b=ecTdmXvbW6l67Xr6a3dPQdcwSbUTUoIqu0budd14MeJe6VpH0PW8vdISsjwLbRtbi hVKjiA556BCVWoLyOZK9AtFTz/WR1rqY5yzrDV4vC2Mur8cHfCecxDkNdLtYBB56yH tF7YCn08wwUMnu0d/jPNLqxOpZheh/p36Eu9N8f0GOW4wb5ECZsClY0rQMmTg1S9KX h5fT56mpap5UO1tj/QxNWsarB6UlOMaxk8KgaG1R7mr8AFwqBc6RAs7VWgaKvvxKDl jtsWPWYDNa2ULcyAvzuPi3J4v/qISoE81jRWoB8SIgbIpq4wCUM6fsQ/1FHBhFlJvT VBwjU+bAXAIzA== Message-ID: <2e749bbc-86d1-4a10-9809-4777bb5061e7@kernel.org> Date: Tue, 7 Jul 2026 09:04:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE To: Kefeng Wang , Andrew Morton Cc: Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , linux-mm@kvack.org References: <20260706111958.3649651-1-wangkefeng.wang@huawei.com> <892b2a73-4dbd-4090-89c5-46929530b855@kernel.org> <9beedaa7-0896-4aa2-810e-26042476e7a7@huawei.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A469D12000D X-Stat-Signature: bn33c4sne8iccoaj5fy98kxxr3jy8gqp X-HE-Tag: 1783407897-477977 X-HE-Meta: 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 G2xy/lk5 Cc7/jZ2yoDt0mwkfPv3xZN+UNgQuO47Ai0OwaFBnKMW9orx9H2oV05MUG9JPcWqg/vRL6GxDAYQSMMn/9zAHEfMAWNMSMep5CTnbgOFKBqViQo38a4Lov5BGquUESdX6Jq3btkaPY9dCfPk9g6D/3BTgP7TymHxGK9FAPUBPaePylDQ0byr5QAQW4tavOIF509zpcyN4X0h/2yFfJ3eYTwjavYbIWVAVZIpPUAJRiajBVraEeMa/QeVTOthPbvXPaYhR8jMatsTK+sD9EudThJR2GjBfLgx+E5U81xLAR97Pv2uUNOI4X4uZlLz+Bk5KSk2lvoUD+WsFmuSTXSO2r3R4txbc5aie5pV+49GzB5YG1eDZN/jxux3NhkQ4LEYwkAbjxOgjZ3wMjzMq4VUZ2NF0gvQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/7/26 03:28, Kefeng Wang wrote: > > > On 7/7/2026 2:30 AM, David Hildenbrand (Arm) wrote: >> On 7/6/26 13:19, Kefeng Wang wrote: >>> pte_pfn() and pte_dirty() have undefined behaviour when called on a >>> non-present PTE. In migrate_vma_collect_pmd(), these functions may be >>> invoked on non-present entries (e.g., swap PTEs), leading to potential >> >> Certainly not real swap PTEs, as the previous function handling is >> >>     if (!pte_present(pte)) { >>         ... >>         if (!softleaf_is_device_private(entry)) >>             goto next; >> >> Only device-private entries? > > Yes，device-private entries. > >> >> >>> crashes from pte_pfn() or incorrect dirty folio accounting from >>> pte_dirty(). Fix both by guarding with pte_present() checks. >>> >>> Fixes: fd35ca3d12cc ("mm/migrate_device.c: copy pte dirty bit to page") >>> Fixes: a3589e1d5fe3 ("mm/migrate_device.c: add missing flush_cache_page()") >> >> I suspected device-private code, but indeed, these seem to be added afterwards. >> >> But a3589e1d5fe3 only moved the flush_cache_page()? So that one seems wrong. > > I couldn't find a more suitable commit, before a3589e1d5fe3, the > flush_cache_page() only called under anon_exclusive, not a device > private entry, so there is no issue. This is the reason why I chose > this commit. What makes you believe device-private entries wouldn't have PAE set? This likely goes back to initial support for device-private. -- Cheers, David