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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7759C76196 for ; Thu, 6 Apr 2023 11:07:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236414AbjDFLHV (ORCPT ); Thu, 6 Apr 2023 07:07:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229814AbjDFLHU (ORCPT ); Thu, 6 Apr 2023 07:07:20 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BAF6DE0 for ; Thu, 6 Apr 2023 04:06:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680779193; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=LSpYEks1T5f1HgeKXvgnDWGtTBs8ltEecfJ6Ag+UgLU=; b=WuYmFnb4aaDlLnQAwIrUUhLTR6eEwE4vokKPWLColy+//AUamCCUyxIH4oNx/Uci+7rE3q RFuHUBvBYF6SOAXDphESKnKq+tqq7Sg3GBbYbF8T5WJmdP8mqARIVtnbvXONTnePJBCnjr ttdxdw44GCTm61OIUGbsKCzfUKuZARM= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-613-jJolPkiZMh25d-WtlECE3g-1; Thu, 06 Apr 2023 07:06:27 -0400 X-MC-Unique: jJolPkiZMh25d-WtlECE3g-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 12FAF3C0ED6C; Thu, 6 Apr 2023 11:06:26 +0000 (UTC) Received: from localhost (ovpn-12-86.pek2.redhat.com [10.72.12.86]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1D3171121314; Thu, 6 Apr 2023 11:06:23 +0000 (UTC) Date: Thu, 6 Apr 2023 19:06:19 +0800 From: Baoquan He To: Eric DeVolder Cc: linux-kernel@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, dyoung@redhat.com, vgoyal@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com, robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com, sourabhjain@linux.ibm.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com Subject: Re: [PATCH v21 0/7] crash: Kernel handling of CPU and memory hot un/plug Message-ID: References: <20230404180326.6890-1-eric.devolder@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230404180326.6890-1-eric.devolder@oracle.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/04/23 at 02:03pm, Eric DeVolder wrote: > Once the kdump service is loaded, if changes to CPUs or memory occur, > either by hot un/plug or off/onlining, the crash elfcorehdr must also > be updated. > > The elfcorehdr describes to kdump the CPUs and memory in the system, > and any inaccuracies can result in a vmcore with missing CPU context > or memory regions. > > The current solution utilizes udev to initiate an unload-then-reload > of the kdump image (eg. kernel, initrd, boot_params, purgatory and > elfcorehdr) by the userspace kexec utility. In the original post I > outlined the significant performance problems related to offloading > this activity to userspace. > > This patchset introduces a generic crash handler that registers with > the CPU and memory notifiers. Upon CPU or memory changes, from either > hot un/plug or off/onlining, this generic handler is invoked and > performs important housekeeping, for example obtaining the appropriate > lock, and then invokes an architecture specific handler to do the > appropriate elfcorehdr update. > > Note the description in patch 'crash: change crash_prepare_elf64_headers() > to for_each_possible_cpu()' and 'x86/crash: optimize CPU changes' that > enables further optimizations related to CPU plug/unplug/online/offline > performance of elfcorehdr updates. > > In the case of x86_64, the arch specific handler generates a new > elfcorehdr, and overwrites the old one in memory; thus no involvement > with userspace needed. > > To realize the benefits/test this patchset, one must make a couple > of minor changes to userspace: > > - Prevent udev from updating kdump crash kernel on hot un/plug changes. > Add the following as the first lines to the RHEL udev rule file > /usr/lib/udev/rules.d/98-kexec.rules: > > # The kernel updates the crash elfcorehdr for CPU and memory changes > SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" > SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" > > With this changeset applied, the two rules evaluate to false for > CPU and memory change events and thus skip the userspace > unload-then-reload of kdump. > > - Change to the kexec_file_load for loading the kdump kernel: > Eg. on RHEL: in /usr/bin/kdumpctl, change to: > standard_kexec_args="-p -d -s" > which adds the -s to select kexec_file_load() syscall. > > This kernel patchset also supports kexec_load() with a modified kexec > userspace utility. A working changeset to the kexec userspace utility > is posted to the kexec-tools mailing list here: > > http://lists.infradead.org/pipermail/kexec/2022-October/026032.html > > To use the kexec-tools patch, apply, build and install kexec-tools, > then change the kdumpctl's standard_kexec_args to replace the -s with > --hotplug. The removal of -s reverts to the kexec_load syscall and > the addition of --hotplug invokes the changes put forth in the > kexec-tools patch. Other than the nitpick in patch 2, this series looks good to me. Acked-by: Baoquan He