From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 06713606A32C for ; Fri, 6 Nov 2026 10:06:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LnIYthTQ Received: by kanga.kvack.org (Postfix) id 9BDC56B05BC; Fri, 6 Nov 2026 05:06:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9961A6B05BD; Fri, 6 Nov 2026 05:06:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 837CD6B05BE; Fri, 6 Nov 2026 05:06:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 489B46B05BC for ; Fri, 6 Nov 2026 05:06:11 -0500 (EST) Received: from smtpin02.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 1614E140CC2 for ; Fri, 6 Nov 2026 10:06:10 +0000 (UTC) X-FDA: 85404263700.02.D5EBB6D Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf30.hostedemail.com (Postfix) with ESMTP id 58DDB80004 for ; Fri, 6 Nov 2026 10:06:08 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=LnIYthTQ; spf=pass (imf30.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 ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793959568; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Px8YGrUbpB2T2jEhenGoA16y8NMxi2MB1FLmbQ0eAMw=; b=3zHb7Vkb8rVcV3GwCSZ4P6rhQPnF4wrLvahywIHjw0epGR7dmfuwRfqIiax97WIEktgCCC 34LvPLaqIlue9VQ4R+fl3/IygLN72eReXbZ5jfONN3bzPdQGjrAKMQBFo9v9B8rVQajKxh EerZ30+aJTjBiEhY8TpJFcdoiFeGJHc= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793959568; b=g3itUqrguasF8etBYHdJeoVjLKqJ0ouIWVwSCbCJDckhOGhOxglyD5VOxDnOfdHuhGt+gg 8e8pLRZ1BhF9uOdtfGJmOeE2PXL6LCfdYp34MP9qVGuNY9fAmWqigVxmzZmpphPJVOWLH0 y1mKB3xP9K8X7OFg+LzdV0TGwOnohxQ= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=LnIYthTQ; spf=pass (imf30.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 (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id DFB7560232; Fri, 6 Nov 2026 10:06:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E68161F008A2; Fri, 6 Nov 2026 10:05:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793959567; bh=Px8YGrUbpB2T2jEhenGoA16y8NMxi2MB1FLmbQ0eAMw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LnIYthTQJEXOjvvLs54ZGX/uUfr0klYw3b86wsbcnRnjMkpBZxFYk4+mow/6/uap8 Ivtt9RN/Kg0Vc9xqaRycTlEc2bPPJKnPZ6QatK+5uisGzt8lOls3vzsRNfvYPei+Gb XU7CLMDzEh5hkUwM5oR8dSDjbO5AXhJfvwxMegtiuS3dtstOuW+UNGQgD3B/Z7aKDc B/jYYug6sRFk+ZM0OhppHwhlPQCm4lPM5vlZE7T20ObUuqvApxXnI/Ra+UjDJ1Tram cJlEkqKW0G6jBDB1Y5PPWZc6twszsfy5hzKboS8hBCJmh0OmA0vOHCV4OrE7HdLivD BIwEstq14SG0A== Message-ID: <086c3d5f-84cb-412b-b61a-8cb3ca3e2e28@kernel.org> Date: Fri, 6 Nov 2026 11:05:54 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/5] mm: limit pagecache folio refcount when mapping pages To: "Jose A. Perez de Azpillaga" , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Johannes Weiner , Song Liu , Rik van Riel , Hugh Dickins , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Jason Gunthorpe , Kevin Tian , "Joerg Roedel (AMD)" , Robin Murphy , Steve Sistare , John Hubbard Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, iommu@lists.linux.dev, Chris Mason , stable@vger.kernel.org References: <20261105-refcount_overflow_stable-v1-0-70b9c655da3e@kernel.org> <20261105-refcount_overflow_stable-v1-1-70b9c655da3e@kernel.org> <528e3a0e-04fb-427f-88c7-63a7f4bbc505@gmail.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-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: bib46k9q1h4surd3cicucyadhwuyiy1t X-Rspamd-Queue-Id: 58DDB80004 X-Rspam-User: X-HE-Tag: 1793959568-542601 X-HE-Meta: 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 dpUpQ4Hf F1KWF/1DA8eRKZvZ9Xts1J0Y1eiY19LyeMtyMia0FGfs/+TpenX6GjVgbLZN4ptM5gTwCFO4HXJH5YdN2kWXH7g5tLbJSoSAJXPMnsSu+BCRQsTja+AYdZdYkK9cZy3+b+P5P5mhA5qvH+UCJwceGa5RQUcyqm3Q9idtWEkL5clTKB+WUH8seqe3OArtHaj22wplaZoJYbMmIUBbJksYR2pqEsdFSqhDBl42PYugciO5ztOOJdVNr4STBsznUDr8KBAOMevgE5EpXL8Avbv8WOTzR5OXvugXlarqASMXmxzA5jn1h9ehrHKonsqx8tXlIhSP4qlXSovKhtRc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/6/26 10:42, Jose A. Perez de Azpillaga wrote: > On 11/5/26 2:10 PM, David Hildenbrand (Arm) wrote: >> With large file folios, overflowing the folio mapcount and refcount >> became possible. For anon folios it is currently not really an issue: >> each large anon folio can only be mapped once into a process. >> >> That's not really big news, but it's about time that we do something >> about it because some modern technology might find ways to abuse it :) >> >> One of the enablers for that was commit ddc58f27f9ee ("mm: drop tail page >> refcounting"), however, file thp support was added later. >> >> File folios can be mapped multiple times into the same process, allowing >> for processes to hold many references to the same folio. >> >> As a short-term solution, let's introduce two folio refcount limits: >> one for ordinary consumers and one for admins. Leave some headroom >> before the refcount goes negative, which we really don't want (having >> the mapcount go negative is also not expected). >> >> Start reporting SIGBUS if we run into limits. When restoring mappings >> from migration entries, instead zap the pte/pmd entry. We allow for >> slightly exceeding the limit to keep things simpler. >> >> This is far from ideal, but better than all easy alternatives we can >> backport comfortably. For now it fixes the big problem: letting >> the refcount (+mapcount) go negative and cause trouble. >> >> This is only a temporary fix, we'll follow up with something better. >> >> While the refcount checks are not required for order 0 folios, let's >> just add them for consistency: each folio_add_file_rmap*() and >> folio_dup_file_rmap*() needs a prior check. > in mm-new copy_huge_pmd() now does a folio_dup_file_rmap_pmd() at fork, > since Konstantin's "mm/huge_memory: copy file THPs at fork like > copy_present_ptes() does". doesn't that one need the check too? Yes, that one will need care as well, thanks. I think I missed it when rebasing on top of the other fixes. Thanks! -- Cheers, David