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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3700AC43458 for ; Fri, 10 Jul 2026 20:30:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2AC656B00B6; Fri, 10 Jul 2026 16:29:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 25D536B00B8; Fri, 10 Jul 2026 16:29:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 124EB6B00C1; Fri, 10 Jul 2026 16:29:59 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id DF7906B00B6 for ; Fri, 10 Jul 2026 16:29:58 -0400 (EDT) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 6E14E404F0 for ; Fri, 10 Jul 2026 20:29:58 +0000 (UTC) X-FDA: 84974008476.15.EF5981A Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf26.hostedemail.com (Postfix) with ESMTP id EC80B140007 for ; Fri, 10 Jul 2026 20:29:55 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=CRblMYXf; spf=pass (imf26.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783715396; 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=Uceh3gpjLST7XLAIXuAF2LqD5TvR9k+/w5GQWdiEcT8=; b=nI+sgyXWHz54ShB4LE958zCttZEyhi9+R0K/xIW4OIRtOG5Y4/OibejaUQHCkhpOBTNq7c 7HlqlBHQfVktNKg+3rbMgRVt5Ht1Cf2uZfTQYbxQxyPxkC4Lka6x6jb3LsHjrdboHW7Zyh xkgqcQQ+UT5Iv3Rznb0A/k/rMIs/s4s= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=CRblMYXf; spf=pass (imf26.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783715396; b=QdF1eS8b1t6EDiVGarn0SXtKgG5k/o4hcPginyF60GRXjFgM1crzmG8C5wR4F/c4QIQheL LrDulauoQCQUI1xxNhx2cRjDlmKclHx6LmoYs8J5E+v0wwfJx+/UZA4JMTud8zkHF+CeTj aOThinY7IobuommVRgsi1bch/HVQWq0= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 74FA86136C; Fri, 10 Jul 2026 20:29:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A96BF1F00A3D; Fri, 10 Jul 2026 20:29:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1783715395; bh=Uceh3gpjLST7XLAIXuAF2LqD5TvR9k+/w5GQWdiEcT8=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=CRblMYXffQi+FIsxfpogDWIha2S8idYY7hlFe/hupRbmmEGTpi6BJ4HWTDByp44h8 /3KRTjFlIkQUy1k+KZfduunfVgWR6YZ2blivarDsUJXjaKDGjX+VaUowKSvDe3Q17Q 2r5q2LUoryHQT1HEWXwjVr9G90Mg+9z9Z6tAEqas= Date: Fri, 10 Jul 2026 13:29:54 -0700 From: Andrew Morton To: Lorenzo Stoakes Cc: David Hildenbrand , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Toshi Kani , Catalin Marinas , David Carlier , Dev Jain , Ryan Roberts , Shakeel Butt , Will Deacon , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/ptdump: always stabilise against page table freeing using init_mm Message-Id: <20260710132954.49c85be140500c59c1fcb773@linux-foundation.org> In-Reply-To: <20260710-b4-fix-non-init_mm-ptdump-v1-1-2d40982c98ec@kernel.org> References: <20260710-b4-fix-non-init_mm-ptdump-v1-1-2d40982c98ec@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: EC80B140007 X-Stat-Signature: diip1k9wbug8jica94e5ei48mbikc4t5 X-HE-Tag: 1783715395-654442 X-HE-Meta: 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 6HSEWH6h XB5e3/bhm4URl36yUgWFokw3ZFZhQWsVLmde83ePxUU+jBHG1qdhCB2K8kcz/XbnE/3zgATUJREupGaskuG7HUF3738FeyuRgstfq0MIhZHwtFJW8WFp2TY9AztXmBOXWye5koSNjrLcGjmWa1t2a7EVCXcInSKb1YB4PAWJCH0G6fMxwDQyhsBsdZKcEodvflrMIv/9LAdy7X/3G/K6kFBzLHcIJTCpwfcoF2zm0lpT0eNsB8oko06D21rVECnxEv9AuidzRenhY6CZPIItxxLKYrvKa2HuA8+nY2blxYyNmViC8HfdXse+4ipvLz+CWiG8W Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 10 Jul 2026 14:29:21 +0100 Lorenzo Stoakes wrote: > x86 and arm64 invokes ptdump_walk_pgd() with non-init_mm mm whilst still > walking kernel page table ranges. > > For x86 this is done in ptdump_curknl_show() and ptdump_efi_show(), the > first passing current->mm, and the second passing efi_mm (we reach kernel > mappings that init_mm protects for current->mm due to x86 cloning shared > kernel page tables for arbitrary mm's). > > arm64 does so via ptdump_debugfs_register(), configured by efi_ptdump_info > for efi ranges against efi_mm. > > The init_mm mmap lock is used to stabilise page table freeing against > ptdump, so take a nested lock on init_mm to ensure that we are correctly > stabilised. > > We take this after mmap write locking the non-init_mm mm. Nothing acquires > the init_mm lock first before locking an arbitrary mm, so no deadlock is > possible. > > Other fixes have been sent which update the two cases which can cause races > with ptdump in init_mm ranges to acquire the init_mm mmap write lock - vmap > and x86 CPA huge page promotion. > > For arm64, commit fa93b45fd397 ("arm64: Enable vmalloc-huge with ptdump") > already provides exclusion against init_mm for the vmap case, which this > patch also pairs with. > > The first point at which ptdump can race kernel page table freeing is > commit b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page > table"), so we target this in the Fixes tag. Does this have any known userspace impact? > Fixes: b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page table") Since 2018, so I won't make this a hotfix, OK?