From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 32E29C04FFE for ; Thu, 2 May 2024 13:47:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C26A66B008C; Thu, 2 May 2024 09:47:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BD77C6B0092; Thu, 2 May 2024 09:47:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AC5956B009E; Thu, 2 May 2024 09:47:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 8E4F16B008C for ; Thu, 2 May 2024 09:47:14 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 47D8DC0E4C for ; Thu, 2 May 2024 13:47:14 +0000 (UTC) X-FDA: 82073582388.18.894E5F6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf03.hostedemail.com (Postfix) with ESMTP id 24D7820004 for ; Thu, 2 May 2024 13:47:11 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=none; spf=pass (imf03.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1714657632; 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; bh=zz5RaZl9k154TDIXcj/FWxczbnfO8VXEFFPMSfS5LqA=; b=Iw2Hruzk3dVul5PCo9TC2+zi6KU7+AcreJOwYt2bZMkp9To+4VxobWjlUuSMTG4HY/JjyM FtkYLWvNrX961WL1w+iylwHQ8Qx/qIlTuRzu5mHxbCyIgWOhEVNiGS4EGv/S6C3n7mN5yc QpzWPl6nqsqNOd0whNx+EB8/v3WDBno= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=none; spf=pass (imf03.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1714657632; a=rsa-sha256; cv=none; b=dBGaRBEfkyCb0PPKbav2G8NkQd1tV/BZE1sdMxQQ/GPBnBP3GqYrvI5zKp3ExE7+74kumt yklK6PXj7vTatAvtPZhnUzmn6hsYzPGXSw5ZmElgyIr/VYjSN/QHYdTPPQLix4O5dlp+8c w1/aP0qhXAjlXQaeK25WBVSeNiJb3Sg= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C48D92F4; Thu, 2 May 2024 06:47:36 -0700 (PDT) Received: from [10.1.37.181] (XHFQ2J9959.cambridge.arm.com [10.1.37.181]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 11C9D3F73F; Thu, 2 May 2024 06:47:06 -0700 (PDT) Message-ID: <60739cf6-42ff-44c7-8e33-6c42eed71a66@arm.com> Date: Thu, 2 May 2024 14:47:05 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm: Fix race between __split_huge_pmd_locked() and GUP-fast Content-Language: en-GB To: David Hildenbrand , Andrew Morton , Catalin Marinas , Will Deacon , Mark Rutland , Anshuman Khandual , Zi Yan , "Aneesh Kumar K.V" , Jonathan Corbet , Nicholas Piggin , Christophe Leroy , "Naveen N. Rao" , Christian Borntraeger , Sven Schnelle , "David S. Miller" , Andreas Larsson , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Felix Kuehling References: <20240501143310.1381675-1-ryan.roberts@arm.com> <3d88297b-ce6f-4b97-8a25-75f0987af6fd@redhat.com> From: Ryan Roberts In-Reply-To: <3d88297b-ce6f-4b97-8a25-75f0987af6fd@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 24D7820004 X-Rspamd-Server: rspam06 X-Stat-Signature: uxcc6tyfxj9ux8ku31xmiam1teem8x7w X-HE-Tag: 1714657631-855823 X-HE-Meta: U2FsdGVkX19HCWICK/jUDKcSMrxzuhBmMDSLtPw5a18h0mh5pfP+xQn4q8MJzgZcvnTamMfTtG12S+qN6Dxnfil746fN2W/l2PwpiwNudugbpWVh2BxWqmyPvWZ88/rkynZgdOu/ke6hpJPX+gDIK1EY83oZkrtJunHHTOCsPGSUbJ3JoLyHWj9zzWRoOElBMw/upJ0A7Sx/4e+1woQqHfOGPV9ZT4zvkHg8HTOkIy0xdpYiLKWAPQBC7zH6E5qpLVpa5V1KOeXVbw2zCtSBAkbWs60wPZFX9d0Q4+WhztCTSqP8CpVqtASBnLNiMlxGKtNraUENhomPHE8L29FFd/UfsTGuhTMQFtGbUTvLy8Bb3aZ9+yRE2fNMtF+SZuW40szmY2XN0uHJhz+98FYDiqSAq7u9OQVSaZ7ZUd3UrnrncMwcSEV1hvb/9jJbssEA/fLwnnz9l92wyqkePElnC6VdfSLbNtuplBCD1vUtDceLbeveQLlXAXbIDWb/65HapvRUn2Jf+7z+yr4BCEs69TURkPS37oxUzohy1LSgmJZmdwZpnqlh36FOmDptMIxR9V8P4zQ8/vu0rKBs1zqi5DHs9LPBqedcs3DQrkRRiC5GWPJWHWdSeql6xFEIeRfMXYBAW1etKkWxe6zYmJ8S8OKM5b5W9lk79OFewwxUyhNF1TcCzhozfHDoCpWY2fi9mI9IZYU5ZcTozzF3RjEUrX+dv49nZt2JghwVwajject2dv4jCd60ICD/csDOz0yLJAZIg1ggOEGIwpIqNMjR18CTaQwtho/vrEcQxvZRC535u5FAAO3qelcYzpdKT+Wer3KOlFNOO+YU8aJ1g3ID9T6GYa/1Cb16Gz0WdyrdBR+sdB5h0wnBTr8WtlwyJbxWbG+mSd0QrdmfQLMInu8PavkiBdVjF7ClXp+vqTmiplA1JcOgUrpBbBixkaN02NweVAo/j5XuL/aJazRHSWn 4tGWc12Y DeCtC4scbiPyryVxOgYt4wFjSNKFZ1Fb7O4BZhAbf+2PkAr4OSE62Woya6vDR81TCM5nENCHYOgl9ES2Cr8PqOzJJ3gOc4zVhjyVazi5gNwvGE9PPfNK29NMUMwgVUujUD4/PM8jAI/mT1IEnULSPnVjxnFfIiZZfV0ChnTR7LULVLcmQ6xS7FsTa9d5RwfvrTrultgJUMIFhnz4RUxjVlaqWTarSRKOVXVQW0TfhhiHcuMVAf8xjSuhdaUzSTixcVbddBg8cTyuyjBnlcsmQrNCuMQ== 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 02/05/2024 14:08, David Hildenbrand wrote: > On 01.05.24 16:33, Ryan Roberts wrote: >> __split_huge_pmd_locked() can be called for a present THP, devmap or >> (non-present) migration entry. It calls pmdp_invalidate() >> unconditionally on the pmdp and only determines if it is present or not >> based on the returned old pmd. This is a problem for the migration entry >> case because pmd_mkinvalid(), called by pmdp_invalidate() must only be >> called for a present pmd. >> >> On arm64 at least, pmd_mkinvalid() will mark the pmd such that any >> future call to pmd_present() will return true. And therefore any >> lockless pgtable walker could see the migration entry pmd in this state >> and start interpretting the fields as if it were present, leading to >> BadThings (TM). GUP-fast appears to be one such lockless pgtable walker. >> >> x86 does not suffer the above problem, but instead pmd_mkinvalid() will >> corrupt the offset field of the swap entry within the swap pte. See link >> below for discussion of that problem. > > Could that explain: > > https://lore.kernel.org/all/YjoGbhreg8lGCGIJ@linutronix.de/ > > Where the PFN of a migration entry might have been corrupted? Ahh interesting! Yes, it seems to fit... > > Ccing Felix Are you able to reliably reproduce the bug, Felix? If so, would you mind trying with this patch to see if it goes away? > > > Patch itself looks good to me > > Acked-by: David Hildenbrand Thanks!