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 2CDB0421A13 for ; Fri, 10 Jul 2026 11:56:09 +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=1783684575; cv=none; b=bSriARM8J99szsjPdCJRkk1JTSDV/DEz0h6ErCdakiYD3J8gEt+Zz6o27lcrekB9s7PI9CwqMKfJgJI6oEPr6i6SDgrOR/bFChp4HHWMigF7CEaR2SaoIprHJE3kvVCjGdmhS8w2pEPSRuPANP/6UJSWzf5OaTHOsx66yyKog1A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783684575; c=relaxed/simple; bh=0mFbBp3P+QqPQISBo/DA24+OlkgLQls3gFhqscsJfwI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JuWYvEtIyUiXjDqq4uSHCf6BR6JQzmxAS9vJl8gwUJrkeqqZcuJa4LaDlGR8hwP+b7gist4CWsIzs7G5FBHpUkIclHYO9LVqN1LvwwfhOCRUV347AsE+FpsSJ61orCE5NRcpiw0bN5OvveyHyWDK42yYjuCeQ7StGeUf9QiY/hw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oTyO2VIx; 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="oTyO2VIx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49D371F00A3D; Fri, 10 Jul 2026 11:56:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783684566; bh=jJGaatRjwBZDaRYFziAGVE6xXbmWCuuBdDrIfUFO1AY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=oTyO2VIxMBB42K5Bhcr9UQREwKDxPuVvC6JA6rtNOikDUoWL2vaTZOpb5Xyze4RJF OolCqpMEokk+TV++qNNsMMR8n5di3mKHo1TcfyFK17cTxuVHCr016+bOS4cDrPpWKD xMJr5JchSMLxDY35RJp9iNhhVWtNbJQlLekNaMEQHExiL1fzHAs/wHrIWIRWNKVyxS khr7n5I1deMjltj/9sJ6lllqcxEMfxwmptTMXXm5TzvtkxyZ+HrboUHd5WVbwaG9Oy gRKu502HExMxvcWAnra/EczpMKplwjyJKfiQ6xMG4dKWpcsRv2hB7zdSu0Xmr+JaxG SgMbQKBQF4uCQ== Message-ID: <89d20411-4915-43e8-9808-3a7fbd98d2ab@kernel.org> Date: Fri, 10 Jul 2026 13:56:01 +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] mm/migrate_device: avoid overflowing migrate_vma collection arrays To: Zi Yan , Andrew Morton , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Balbir Singh , Kefeng Wang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko References: <20260707-fix-array-overflow-in-migrate_vma_collect_pmd-v1-1-ce3ff4627653@nvidia.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 7/10/26 13:30, Zi Yan wrote: > On Wed Jul 8, 2026 at 10:43 AM EDT, Zi Yan wrote: >> On Wed Jul 8, 2026 at 10:35 AM EDT, Zi Yan wrote: >>> >>> I guess I have the same feelings. >>> >>> You mean we reset migrate->cpages and migrate->npages and restart from >>> the beginning? But it is not only that, since the code below also >>> changes PTEs into migration entries. We will need to revert them as >>> well. >>> >>> Hmm, migrate_vma_collect() documents itself as "update the src array and >>> "takes a reference on the page" without mentioning changing PTEs. I >>> wonder why changing PTEs is necessary, since later migrate_vma_unmap() >>> also changes page table entries to migration entries, although >>> migrate_vma_unmap() changes all entries to a folio, whereas >>> migrate_vma_collect() only changes PTEs from the specified VMA. >> >> OK, it is an optimization[1] when migrate_vma*() was introduced. If >> there is only one mapping, migrate_vma_collect() will set migration >> entry immediately without waiting until migrate_vma_unmap(). Fun. >> >> [1] Commit 8c3328f1f36a5 ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") > > Hi David, > Hi, > Do you think this patch is good to get in? I would like to get ack from > you. I dislike that we fail collecting even though there is something (different) mapped now. In case we stumble over a PMD, there sure are no migration entries on the PTE level anymore? -- Cheers, David