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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id EF238C76196 for ; Thu, 6 Apr 2023 11:06:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=YRxkmUap4nYl2byta7y9I8el93XlQW8hXuzTotvDiC8=; b=UxyMEd29q/6lgw ZODQjP1dPXApf2ETQew9FYrr/kKQH/iGJE1IuttP2AjGa89m8BpD3fl2LJRP4ZS5S/21O6vxxU7SO R1cqlDIYP3iQD/MLJQ+9JuQEXUeCP8C1LJ57PZYcV6kdHyRDJJkul5V5Qi/1pOLWbMmsm1Oc8hd/U Z7dp8hHF8ENC9d1OONtSSlUDQbDgFk++ne4DAJAIlqk6SOZzDA4V7t6raHBg1HKh2ANqsoF9zqBHK /0ZMjDr+pLgpZ0qoN5qjpQU4bv1YHqx7wMiaSaftx6KmSWcaFwjoKgrSIjMHovdZgFnKrtSqMe72c r1jsVqvA84lfNvBYYrXw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1pkNRs-0077Cy-2v; Thu, 06 Apr 2023 11:06:36 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1pkNRq-0077C0-0Q for kexec@lists.infradead.org; Thu, 06 Apr 2023 11:06:35 +0000 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-Disposition: inline In-Reply-To: <20230404180326.6890-1-eric.devolder@oracle.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230406_040634_238904_407D088B X-CRM114-Status: GOOD ( 26.17 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.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 _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec