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 E27B4606A328 for ; Thu, 5 Nov 2026 20:25:19 +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=y2hJTr5z; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=NCMd5EQd 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=A/5VT3V/dJzwpelYcF9cS6x7xpOutBaEMG5KLkPXIhM=; b=y2hJTr5zsQ75Kh692lu7GZKwH3 LjL7tVqubP8eM79clqWOBcseqXlNMSvFB4wcUYlJTFF/cjSZ54hWLFSjutCGhv8r0MF+il2lXbQq+ 1Aj+EhyUpS01dynaMJGrxgDGWjFn4MPrRCxM0oxMyJ47yqqmhn/gdGLm0HEBDuYBCr9q127/pYBxl M+mTKJpWa2b5J3XRXhJpZOT0C4Dw1JVAbyYNqdFGyulG9/mK9pjJePqrqWQrFHVukvX3W3Gzd+XKo X8hfvgB0chd+llFEIkTv5QtjLwssqA4+5Mh43LMQgHPGWkRNScGZ/oW2nZtNqQNLLEKMjGNrBZV9n xXli0wHQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xP3CI-0000000ALju-1sxs; Thu, 05 Nov 2026 19:32:30 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xP3A2-0000000AKl0-2D9N for kexec@lists.infradead.org; Thu, 05 Nov 2026 19:30:10 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 48D694398F; Thu, 5 Nov 2026 19:30:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A439D1F000C1; Thu, 5 Nov 2026 19:30:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793907010; bh=A/5VT3V/dJzwpelYcF9cS6x7xpOutBaEMG5KLkPXIhM=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=NCMd5EQduKiSLAcILn4CM/ObnRlBb+kiiI+/5ab849SU4+HjXc1QOgHqSAh7M6E27 b+FiWMO6CLjTXf1Nj4CyvKUhbV9P2lO6Ravfz73arpAD6MqZyaeurUt1DmNcp2r1xg UEtfUQQPAMqtvXYriH4kf04yzM1YNYSXVxflhjmEiLm3NIsLubCTc7B6pP89rAaYC7 vRhscV5ISjyZDOGiESm5OMRWASt0Bg48G9OtHsxwoa1X79Gw2jkS0KmKoFwLBKiagJ sc5Nah8PodeqHU5rOOtjTf5ulsejQkKKP0tx0YH8oCfD6kQ7LV1Lc6tg+oT5rHUsp4 dLpYzKAb3IJeA== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH RESEND v2 39/51] 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: <20261104-work-procfs-bugfixes-v2-39-021c84d852e0@kernel.org> References: <20261104-work-procfs-bugfixes-v2-0-021c84d852e0@kernel.org> <20261104-work-procfs-bugfixes-v2-39-021c84d852e0@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Thu, 05 Nov 2026 19:30:07 +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, and those have been memcpy() for as long as > copy_oldmem_page() has had its kernel buffer branch, since commit > 54c32021eb6f ("[PATCH] powerpc: Add arch-dependent copy_oldmem_page"). >=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: 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/20261104-work-procf= s-bugfixes-v2-0-021c84d852e0@kernel.org?part=3D39