From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AC30B606A323 for ; Thu, 12 Nov 2026 16:50:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=Tym4gkjQ; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PYDTrptA DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Reply-To:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:Date: Content-Transfer-Encoding:Content-Type:References:In-Reply-To:Cc:To:Subject: From:Message-ID:MIME-Version:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Unsubscribe-Post:List-Owner; bh=TwZA6J1WWNQirUHO6lcSIfw8e+F+eLWDt4uPBoTdUYA=; b=Tym4gkjQW2gGs+HMmaI5EJBasI GW0QOjvrri4XJwdHTyepk/CzLqP9q1okWITJcFrI6Pz7ojf+jdiQ0e9Z9frv8Yi68nlE8uVdPA8+Z nIhxXitaHG1PHGo1lARMcleJ1hzBD779g+0KKwM8U3jqP8fLr54fqBtGWCGL64ybZAO4NOoAnWwXT mw4z2k17JvLBkezCDHQG7IolyLFhZe9j4g+NQ6Ypbns+sO8S3JcQeZmHPcKQP99RBIWMxqaFm+Uh+ GYe+uDqunuymYyI75U1ysFEfucmAFcN4OUzx+6sy5JpOIIsieH61t7ofNVlXIt8/bETQNUhx28Mg9 HzTwdo+g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xRY0p-0000000AgKe-0ZP7; Thu, 12 Nov 2026 16:50:59 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xRY0n-0000000AgKR-3wKh for kexec@lists.infradead.org; Thu, 12 Nov 2026 16:50:58 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id B4EFC60224; Thu, 12 Nov 2026 16:50:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 097511F000C4; Thu, 12 Nov 2026 16:50:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794502256; bh=TwZA6J1WWNQirUHO6lcSIfw8e+F+eLWDt4uPBoTdUYA=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=PYDTrptAlOLs8mQoy3QgA75QPbqhIMrnLgowg3I9BLU6ENeQUCozkSTDdKvFGo6iS HHRmQS2mZGLttM9mvfc0xRYmeuzrfGvhDdOecrkORx+kTTGAV5+QuufluZuWgcvkxW kTTf6LT2aE9yh4b3jclOflFm/98E0LCoMJBqiCGdl5LEVIwNGcT/5fWFWOMjYWLckQ uLdN+amSDJE+vmlYSkC3DlRCMUQbCIxLdnM3jGugd5uyhLs6A+aIumfZUh4CPr4Chg Fwi2Pm6Dij9KW95E/jpZY24SbhlA7ApWAS//9x1yVouofFGb+ryCDddNI2YLIqAeix 3Y2PWeBJ9NRkQ== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH RFC 3/4] crash_dump: recover from a machine check in copy_oldmem_page() To: "Christian Brauner" Cc: "Linus Torvalds" , "Breno Leitao" , "Chris Mason" , "Thomas Gleixner" , x86@kernel.org, kexec@lists.infradead.org, "David Hildenbrand" In-Reply-To: <20261112-work-procfs-oldmem-v1-3-ecdcafd99265@kernel.org> References: <20261112-work-procfs-oldmem-v1-0-ecdcafd99265@kernel.org> <20261112-work-procfs-oldmem-v1-3-ecdcafd99265@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Thu, 12 Nov 2026 16:50:55 +0000 X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: sashiko-reviews@lists.linux.dev Sender: "kexec" X-Spam-Status: No, score=-10.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 X-Archived-By: > A capture kernel reads the memory of the crashed kernel, and that memory > may well have uncorrectable errors. That is after all what the first > kernel often died of. Every architecture that maps a page of the old > kernel and copies it out does so with copy_to_iter(), and a machine > check in that copy takes the capture kernel down. >=20 > On x86 a machine check in the kernel is only recovered from if the > instruction that took it has a machine check safe exception table entry > or copies from userspace (cf. error_context()). The copy of an old page > is neither. Its source is kernel memory, whether it goes to the buffer > of a read() or, since commit 4a22fd20379c ("vmcore: convert > __read_vmcore to use an iov_iter"), into a kernel page for splice(), > sendfile() and copy_file_range(). So a read of /proc/vmcore that runs > into a poisoned page panics the capture kernel, and so do vmcore's own > reads of the ELF headers and notes. Breno sees the result on a fleet: > [ ... ] > Fixes: 4ae362be5093 ("[PATCH] kdump: read previous kernel's memory") > Fixes: 54c32021eb6f ("[PATCH] powerpc: Add arch-dependent copy_oldmem_pag= e") > Fixes: 4a22fd20379c ("vmcore: convert __read_vmcore to use an iov_iter") > Cc: stable@vger.kernel.org > Signed-off-by: Christian Brauner (Amutable) Sashiko has reviewed this patch and found no issues. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261112-work-procf= s-oldmem-v1-0-ecdcafd99265@kernel.org?part=3D3