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t=1788961389; bh=u9IzuLqDULcD860ya5R4OSTfR5VByrothjUZYfYv1/w=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bYS5kG7e4E5j8HFOwgf2LIOyXcy4a25Yvc6Y3XLeFu/8a6PVFx5B8WYOyEcjewUmN jW04ZRymPTZpVDoUmqfDccKEUeB5BYifKEsEnkZLavCGdl1YJoXuSFHw5/iP4rh8bm b/MvS25hdYpQcmIDoxo8wNMc49Zag720BJ14WBnnXFMhIepMzJnC6cVPmBbqAGBmae L+O75kGdtiB9bCj3zQ3gHtPxeNhkWWZj3f/pVVO0w/X01GKjqpyFz119ULV9Ni8qKL GVGRjlcWOpw/1/1Wtk2u5XncOGCx2VsNxZiDLmLDr0/u7EhyVPP+jieu+t+3X8AojC Q4XS3SO9cicrw== Message-ID: Date: Wed, 9 Sep 2026 15:43:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/migrate_device: avoid out-of-bounds writes for compound folios To: Hui Su Cc: Matthew Brost , Andrew Morton , Balbir Singh , Zhi Wang , Joshua Hahn , Rakie Kim , Byungchul Park , Gourry , Ying Huang , Alex Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260817120758.669807-3-sh_def@163.com> <4ead5df7-f000-4087-83e4-13aae036e0b7@kernel.org> <5ae7a11c-1db4-44cd-bf67-a98cfd5ca08b@kernel.org> <20260909112049.3202956-1-sh_def@163.com> 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-Server: rspam10 X-Rspamd-Queue-Id: 17DFDA0006 X-Stat-Signature: tak19oucd6tw8kwqhaugpit7ppiag4m1 X-Rspam-User: X-HE-Tag: 1788961389-123724 X-HE-Meta: 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 KuvgFDED JOy6aRyUTeIz/qhZ6Qkmq2uH1UC7hh3YSDEncYD8A5ZHeyoclPGajAftuqjs6Zeoj//ZdsgiTd++9+l8sRO9+9ylBdJ5SlMGf9zltUmNWh5s/3SrMr4RY8ilwG61uvCmNhJAEykTDCPvrb9CpUrLITQFzdg3ksootJ02+QkOF2wzC4YbuA61i4UUJdPouqmOuXbyYrKtCc/njBEAMdFrgGz31MU1VvVDVunsUGK5KfQD84lz9ShXpmTTzeqYEZp9hC92bGZJQ2Iiz5HgbBKXJEi2Kras1Imq3mxAwvQe6Kse27Ixyohsfa++3HsQ05QSrHBHo9LAZmwY/rcz6cBajQKQqi8n9PiCxqVD7qkL3yHWXN8REBzuZ2a5Z04mW8wEDG08h Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/9/26 13:20, Hui Su wrote: > On Mon, Sep 07, 2026 at 02:23:33PM +0200, David Hildenbrand (Arm) wrote: >> That's what I was thinking: because how should we partially migrate folios? >> Doesn't make sense :) >> >> If this cannot be triggered today, neither Fixes: nor CC: stable is appropriate. >> >> Agreed that we should just warn. > > Hi David, Matthew, > > Sorry, I missed this earlier. > > This fix has already landed in mainline, but I agree that the API semantics > should be clarified. Partially migrating a compound folio does not make > sense. If the intended contract is that callers must not provide a range > that cuts through a compound folio, then treating such input as caller > misuse with an explicit WARN/error path sounds reasonable. > > The reason I added the Fixes tag and Cc'd stable was that I observed an > actual KASAN out-of-bounds write with the HMM migrate_anon_huge_zero > selftest. The path was: > > dmirror_fops_release() > -> dmirror_device_evict_chunk() > -> migrate_device_range() > > My intent was to prevent migrate_device_range() from writing past the > caller-provided src_pfns array when such an input is observed. That said, > silently stopping the collection is not necessarily the best API semantics > if this should be treated as caller misuse. > > I will rerun the reproducer on current mainline and report back with the > result. If the preferred direction is to make this an explicit WARN/error > path instead, I can send a follow-up patch on top of mainline. Yes, and please clean up the code in any case; the duplication should be avoided. -- Cheers, David