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 7629D3C0608; Thu, 25 Jun 2026 10:38:01 +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=1782383882; cv=none; b=UEUOHH+Zuf55p0nlZyajBI4xYO4+8VMq2hfOP5wsedEU2iKdf6rgQJtxEUSGIevTrGj5e5eCkioO1FVz8mG/NNIVcgTBuMLQgkDr5lSnJcXphOgphp8y3OtSDp6Bj7DblHoQJdYZ+JgqNNc+yF80j41KzJkx/pvsFPt5BfE9qUc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782383882; c=relaxed/simple; bh=5Fl6NouESQ4crH8IyBdbpaTzpYkZVdEUlYrjCsfBzRg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ciN+WfmEpW0G1dvlIpyH+J3VJ7n4UCvbNemJdZYN02gIvk+h2mVsRgm8IJq3JRPKfW8LHL2KCS53tzxI3qTQ8XVonOBDlj9gjrSAp5FPot4C7xTPRzMA36eJslSpIne2yhvAJlWjE8BZWd3b9S42jGVgezRhN0r9BLZ3oskf0lg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Lfka2xAB; 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="Lfka2xAB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63F861F000E9; Thu, 25 Jun 2026 10:37:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782383881; bh=fJ5GdqfFbLqq0HefJ/fPOXSGHIZ3giq6UVgT6Fg0adg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Lfka2xABH4WlCH4+Kcss1VPXGMllQT4xshc3EanCjCi2KvTd4/QdGhadS1atYJxN9 4QkETM0uJkIzS9CERgnRpjWb0kDTrRBCffxgEc9S+X4SoqsI6SLDXzW+/JyjPofaJm TzK/U7C0PBQwZKaToMx+Vqy0eEdZ0iAeNKWhQHStqLyYV7eGzhVXikwfiMCSJCs7xR Qiqp57S5pu7nnGzKbPyFYU/5kcXyA2Sr1GQWZC61FlnjjkdAtXq1aGCfXkVIg8Z01x un+M6OSbEtVRK4P3KbjkTPPG7d2HH/Y9pcfvKMBzmS/vt7xX+4XWEdfBKQBH31mfEy Uwj5mmyWpXBbA== Message-ID: <2252683e-df5d-47ce-b15d-1036bef8d063@kernel.org> Date: Thu, 25 Jun 2026 12:37:55 +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-hotfixes v4] mm/page_vma_mapped: fix device-private PMD handling To: Wei Yang , Lance Yang Cc: akpm@linux-foundation.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, ziy@nvidia.com, sj@kernel.org, balbirs@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260624065353.1622-1-richard.weiyang@gmail.com> <20260624085756.6598-1-lance.yang@linux.dev> <20260625095728.woikmkxb6gskth3b@master> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit >> CPU0: pmde = pmdp_get_lockless(); // sees PMD migration entry >> >> CPU1: remove_migration_ptes(src, dst /* device-private */) >> ... via rmap_walk(dst) ... >> page_vma_mapped_walk(&pvmw /* src, PVMW_MIGRATION */) >> returns with PTL held for the PMD migration entry >> remove_migration_pmd(new = dst page) >> installs a device-private PMD >> next page_vma_mapped_walk() >> drops PTL via not_found() >> >> CPU0: takes PTL >> pmde = *pvmw->pmd; // now device-private PMD >> >> So when PVMW_MIGRATION is not set, current code can return not_found() >> before we even decode the locked PMD as a device-private entry. >> >> Commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration support >> device-private entries") made the >> >> device-private PMD <-> PMD migration >> >> transition possible. Doesn't the folio lock help here already? -- Cheers, David