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 A79BD606B277 for ; Tue, 3 Nov 2026 14:48:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=IKG97VAS; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LexbkyPl 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=/kElDKkabdJCRO6xnlGV31zxVfj0y3IarZ4wubDtz0o=; b=IKG97VASIW7nr8dJttanUo3vc5 g8KfT+mb16l5sqNv9U8qLEmwwzDmRev5+oG3KCUWngFG6P1+RSVck28ztLutFWN3as90I4A2tuR3Z 2Tqu0oZVmNxxgSKc2dHXzcLaBGCgncqFF/5dEooSBzHbC9W9P9ARLvDKDjM8pzMolmJX9HMKRi7V2 w350ESOSqkzPy55/J9d5YeHxGiiMlNV9/XPITasei+mkYJh6JQ+o67La6wneee/u2AzzNjGT7OrdH rlXV7us7kEYoLdjFyWcd16j1Fq+UuFZ7UXenH2D/IC9014f3hsvq5mc2EppgeKf9IywI8OiNxobTh Eo34t0bw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xOFoJ-00000002lY5-0T0y; Tue, 03 Nov 2026 14:48:27 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xOFoD-00000002lQR-0VGx for kexec@lists.infradead.org; Tue, 03 Nov 2026 14:48:21 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 8EC27609A2; Tue, 3 Nov 2026 14:48:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F41511F00A18; Tue, 3 Nov 2026 14:48:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793717300; bh=/kElDKkabdJCRO6xnlGV31zxVfj0y3IarZ4wubDtz0o=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=LexbkyPlz2zQIYc8bF2pRjKX/AkvfQPkVIaTn+eJLpPY+XRILitZ5nAWg6f3Tusuh HQNETtvJbmEhM0aoKtzkgu0kgjOexpa4LlDw0I6/3+mwhTU3usX4A/HlO3gr8J6oLM IgH6VaEhvysagiE3cAOglcKn4CUmS6tVKtwMnQexbp3BGK7R3zHHh+uU933vnYx9Ua HvERM1FpNfN9QoeRRHMNLIBS3U06l9Wt5PRzW5n7A08d1qMfsTfUwwoEI1pq6/YOvV 5vPuxcrk8/zjzD9bphuDNnUp+Mj8VlIBw+rT8egZkVw3b5mCtS0M+aGGgGqwKCSnhr y91xEUDL0eaDg== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH RFC 26/38] powerpc/crash_dump: recover from a machine check in copy_oldmem_page() To: "Christian Brauner" Cc: "Linus Torvalds" , "Jann Horn" , "Josef Bacik" , "Chris Mason" , "Jeff Layton" , NeilBrown , "Eric Dumazet" , "Thomas Gleixner" , "Al Viro" , "Jonathan Corbet" , "Christoph Hellwig" , "Greg Kroah-Hartman" , "Joel Granados" , "Kees Cook" , "Jan Kara" , "Jan Kara" , linux-s390@vger.kernel.org, coreteam@netfilter.org, kexec@lists.infradead.org, linux-pci@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-usb@vger.kernel.org, samba-technical@lists.samba.org, linux-m68k@lists.linux-m68k.org, linux-serial@vger.kernel.org, "Takashi Iwai" , linux-ext4@vger.kernel.org, "Chuck Lever" , tytso@mit.edu, "Heiko Carstens" , "Vasily Gorbik" , "Alexander Gordeev" , "Christian Borntraeger" In-Reply-To: <20261102-work-procfs-bugfixes-v1-26-59422ed3e465@kernel.org> References: <20261102-work-procfs-bugfixes-v1-0-59422ed3e465@kernel.org> <20261102-work-procfs-bugfixes-v1-26-59422ed3e465@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Tue, 03 Nov 2026 14:48:18 +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. On powerpc a machine check in the > kernel is only recovered from if the instruction that took it has an > exception table entry (cf. mce_common_process_ue()). copy_oldmem_page() > copies with copy_to_iter(). For a read() of /proc/vmcore that is a user > copy, all of whose loads have exception table entries, so the machine > check turns into a short copy and read_from_oldmem() returns -EFAULT. >=20 > But since commit 4a22fd20379c ("vmcore: convert __read_vmcore to use an > iov_iter") /proc/vmcore can be spliced too, and splice(), sendfile() > and copy_file_range() copy into kernel pages with memcpy(), which has > no exception table entries. A machine check there panics the capture > kernel. The same goes for the reads of the ELF headers and notes that > vmcore does itself. >=20 > Copy with _copy_mc_to_iter() instead. PPC64 selects ARCH_HAS_COPY_MC > and there it uses copy_mc_generic() for kernel and user destinations > alike, which has the exception table entries. Everywhere else it is > _copy_to_iter(). >=20 > Reported-by: Chris Mason > 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/20261102-work-procf= s-bugfixes-v1-0-59422ed3e465@kernel.org?part=3D26