From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8ABD2560AA6; Wed, 9 Sep 2026 13:43:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788961390; cv=none; b=XtNyOMxtMQVcaBWTva2usO2+sRDJBk3UMr1ryGFfk0hCh/0fEz/9ApH2EZZx+5fv8S0/dFaCUst3wO3xcItNWnEoVlU7jytJT3Ha1TgHlbxEMQ/d6fAR/j9QoKOYl+RTtFbef8zw25UhZAqRFgpf09ws3zyklazKHKEy73EANuI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788961390; c=relaxed/simple; bh=9D2VrtSgIjh+ekg7GYIMf9QvBaRe/5WJyBHjk6U5njY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=FB7FgPODK6yCD2vvmb6DpGuy3EKLaK8Pn8zmO8VwK8jdxVjo6EopfPeJCdZ5Ytlk+aBH8mqILremowZi/whWM0vR6/1CzoUbu9dNdgYHugEirPGTxG8qNcyLfl65eU/EWT9IeA05TZSM8Gyaaz3SnqJb0MqtOVHHZzjTjMPe1x4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bYS5kG7e; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bYS5kG7e" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3DA481F00A3A; Wed, 9 Sep 2026 13:43:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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