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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 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 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 7AAD520002 X-Stat-Signature: uheuc3uhyy9ziuc3fbypp1pchiq3beqi X-HE-Tag: 1783684567-901131 X-HE-Meta: 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 56DGvL9R tCGTBU5u7h8msQ6QwADkN9qodZ3POLtl091pb7McxijcQtIwrvnRE68LprnXxZ5lPhXrM8kpqtYOtwXFT8xsxqSKDv3OsRABpIIZavZSoh8XxgWHpqDs2eR4hzoK/JezxpNxLPtsxMghuyibd0MQX9L/Zq2Be40ni3fo63fywYz5sI6vllxdaKmaw1zjXwiLD60ZB5sv3OeWwVQ9hkhV3n6RG62yIIlYmukEJ9yq3RrSCjBBt0S7xU6qdhWRn/UPAPUITkkoK9bNxLnBnub7m6paaDb4T1DQjw9NAy6MYOnrjAowj6SD2OqUlx5vAEsX7QcID7oyljreNyJ/rC9jIjmaiBBt/8GTibbtB50TNJhlUn6Tevd3+bjJ5LOHLXt9/UIsX Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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