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s=arc-20220608; d=hostedemail.com; t=1768560685; a=rsa-sha256; cv=none; b=44QVGgAsbJdz1MU1uYw3pGBSY1fyRp64nQINE++us52rib8G78U/4G5/qcNv0ktCAl4HkH IonmKH/RL64fhJs0Ep47JJcxNo11u0IDFqCCTT6FB8GLVXgGRALOIMxrPFMWnMiSxMJkZg K6EKeSvjLXIvCtlghI9oc2UKep+VsFM= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=D7lZljhE; spf=pass (imf11.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 16E5660160; Fri, 16 Jan 2026 10:51:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A495C19421; Fri, 16 Jan 2026 10:51:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768560684; bh=rFY9xlBxTcO5q7oAPkLGToaIjHoIexlwDVGdEZseowE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=D7lZljhEaM8EZsQZkib/DBBz4E2jIkdHSOXRdXaT3UyzCaw1B043eK/BUrQfGXKQD WYufWQmpgBxWLs0vBWa4it1La8XZaoby0CPydcmctlompiEpR35FLxgovt7jQ1KSSj n+RnWxxw2P8Zm79JddxnB1y/hGjRdlDQw/m3IsA/2Pw3dPLD2tBbPoZZbyNf/yWPmY //WZsrdDMZFsTlpsy+WcjjThVDXHRLKlKyvZu2Mu69L9WPxbXtu4QEvLlKoQ9r9YpQ L6k6X0pf/YkbeKRyPt6zA1FZGrmvCr27y/d3+vszoGnqUH/2OV6GwOq2DJcHEUiMMX m9+3TDLV3emvQ== Message-ID: <5af933d1-8c64-4d3c-b835-d90c8e9f771a@kernel.org> Date: Fri, 16 Jan 2026 11:51:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable] mm: Fix uffd-wp bit loss when batching file folio unmapping To: Dev Jain , Lorenzo Stoakes , akpm@linux-foundation.org Cc: axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, ryan.roberts@arm.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260116082721.275178-1-dev.jain@arm.com> <343f8462-44fd-4190-9fe2-8120b5403269@lucifer.local> <4b784eef-e874-45a6-828a-4fc2acab6fb7@arm.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D383140008 X-Rspam-User: X-Stat-Signature: hjyt4mpr5jkp3hrj9bkmj633gdfda6as X-HE-Tag: 1768560685-912397 X-HE-Meta: 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 i+D73nd4 oUDwQv+eEhxSdrFWDf9+T5TviErKKpKmONNzkVxVKvFaQXu3A9AjIeSWTXpZqdYKRIy6op4a7tHx6Ju4RNrqEPCCxw+/ywwXaSd+RVn01yte3tYoOMq95/9r1VPZMfF3use5QWKs8Oza+pPyYjgo6i3upa+1zgJS1Df/aP5gKb9v+3hSrD5lEbhdOibANkmMCQjPuIiXU56VrP14KaFALxpOZYI/QzWloOsOa5ctUXAmHkIQnK7q+a4ex0cxERvtcfHpB X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/16/26 10:40, Dev Jain wrote: > > On 16/01/26 2:09 pm, Lorenzo Stoakes wrote: >> On Fri, Jan 16, 2026 at 01:57:21PM +0530, Dev Jain wrote: >>> The recently added file folio unmap batching support forgets to update >>> pte_install_uffd_wp_if_needed(), which still updates a single pte. >>> We end up jumping to the end of the folio in page_vma_mapped_walk(), thus >>> setting the uffd-wp marker only on a single pte in the batch. Fix this by >>> passing nr_pages into the function, and set the uffd-wp marker on all ptes. >>> >>> Note that, since the nr_pages passed to this function is always derived by >>> some sort of batching, it is guaranteed that the set of old ptevals of the >>> batch have uffd-wp bit on all ptes or no ptes, therefore it is safe to derive >>> the value of the local variable "arm_uffd_pte" from only the particular >>> pteval passed to this function, but apply the result on all ptes of the batch. >>> >>> Use set_pte_at() in a loop to set the markers - we cannot use set_ptes() >>> as that will increment the PFN, but we don't have any PFN to update here. >>> >>> The userspace visible effect of the bug is inaccuracy observed by workloads >>> relying on uffd-wp regions to install their own pages. >>> >>> Fixes: 8798e255b5ec ("mm: rmap: support batched unmapping for file large folios") >> Hmm this patch isn't upstream yet, so wouldn't this patch be better as a comment >> replying to the series so it can be respun? >> >> You only do a fixes tag for either upstream things that obviously have to stay >> in place or perhaps things in mm-stable immediately prior to merge window that >> can't be adjusted. > > I saw that the last comment on that series was more than a week back, so best > thought to just do a folded fix on top of it - and I had formed the impression > (from the conversations on list) that akpm prefers fixes over respins : ) That series is still on my TODO list and I hope Andrew will keep it out of stable until I get to it. Hope is all I got ;) -- Cheers David