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[2620:137:e000::1:20]) by mx.google.com with ESMTP id bh3-20020a056a02020300b003816043f15asi25269562pgb.847.2022.03.31.05.58.37; Thu, 31 Mar 2022 05:58:51 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=SClIeyHg; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234638AbiCaKgH (ORCPT + 99 others); Thu, 31 Mar 2022 06:36:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57904 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234633AbiCaKgG (ORCPT ); Thu, 31 Mar 2022 06:36:06 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 2D6E12042A5 for ; Thu, 31 Mar 2022 03:34:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1648722857; 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=ozBz5xX3/M+McvlsixTHsMYnNatIyrKEH4e0NxR73NM=; b=SClIeyHg4DYmfnGFE5ZVavYqWPxJV1Or0GPGlZ2QX1ZfCqZcLiM73L/5FMZ1gO0N5G0vVH 688a5Sfo6hfHN5tL8CTEpcj2dGdEunWFco4XdKTvU8J2K29PLGAyY/NyWJqomDjZrcmLmW ob3lZ8QpfAEU7Y6U6TotHhw4zeFDCx8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-600-DYmwmN4pNKWxFbzr-7pX7A-1; Thu, 31 Mar 2022 06:34:15 -0400 X-MC-Unique: DYmwmN4pNKWxFbzr-7pX7A-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C57BC811E78; Thu, 31 Mar 2022 10:34:14 +0000 (UTC) Received: from localhost (ovpn-13-26.pek2.redhat.com [10.72.13.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BB0DA41136E0; Thu, 31 Mar 2022 10:34:13 +0000 (UTC) Date: Thu, 31 Mar 2022 18:34:07 +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, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com Subject: Re: [PATCH v5 7/8] x86/crash: Add x86 crash hotplug support for kexec_file_load Message-ID: References: <20220303162725.49640-1-eric.devolder@oracle.com> <20220303162725.49640-8-eric.devolder@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220303162725.49640-8-eric.devolder@oracle.com> X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/03/22 at 11:27am, Eric DeVolder wrote: > For x86_64, when CPU or memory is hot un/plugged, the crash > elfcorehdr, which describes the CPUs and memory in the system, > must also be updated. > > To update the elfcorehdr for x86_64, a new elfcorehdr must be > generated from the available CPUs and memory. The new elfcorehdr > is prepared into a buffer, and if no errors occur, it is > installed over the top of the existing elfcorehdr. > > In the patch 'crash hp: exclude elfcorehdr from the segment digest' > the need to update purgatory due to the change in elfcorehdr was > eliminated. As a result, no changes to purgatory or boot_params > (as the elfcorehdr= kernel command line parameter pointer > remains unchanged and correct) are needed, just elfcorehdr. > > To accommodate a growing number of resources via hotplug, the > elfcorehdr segment must be sufficiently large enough to accommodate > changes, see the CRASH_HOTPLUG_ELFCOREHDR_SZ configure item. > > With this change, the kexec_file_load syscall (not kexec_load) > is supported. When loading the crash kernel via kexec_file_load, > the elfcorehdr is identified at load time in crash_load_segments(). I tune the log a little, please check: [PATCH v5 7/8] x86/crash: Add x86 crash hotplug support for kexec_file_load For x86_64, when CPU or memory is hot un/plugged, the crash elfcorehdr, which describes the CPUs and memory in the system, must also be updated. To update the elfcorehdr for x86_64, a new elfcorehdr need be generated from the available CPUs and memory. The new elfcorehdr is prepared into a buffer, then installed over the top of the existing elfcorehdr. In the patch 'kexec: exclude elfcorehdr from the segment digest', the need to update purgatory due to the change in elfcorehdr was eliminated. As a result, no changes to purgatory or boot_params (as the elfcorehdr= kernel command line parameter pointer remains unchanged and correct) are needed, just elfcorehdr. To accommodate a growing number of resources via hotplug, the elfcorehdr segment must be sufficiently large enough to accommodate changes, see the CRASH_HOTPLUG_ELFCOREHDR_SZ configure item. With this change, crash hotplug for kexec_file_load syscall is supported. When loading kdump kernel via kexec_file_load, the elfcorehdr is identified at load time in crash_load_segments(). > > > Signed-off-by: Eric DeVolder > --- > arch/x86/kernel/crash.c | 120 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 120 insertions(+) > > diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c > index 9db41cce8d97..5da30e2bc780 100644 > --- a/arch/x86/kernel/crash.c > +++ b/arch/x86/kernel/crash.c > @@ -25,6 +25,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -398,7 +399,17 @@ int crash_load_segments(struct kimage *image) > image->elf_headers = kbuf.buffer; > image->elf_headers_sz = kbuf.bufsz; > > +#ifdef CONFIG_CRASH_HOTPLUG > + /* Ensure elfcorehdr segment large enough for hotplug changes */ > + kbuf.memsz = CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ; > + /* For marking as usable to crash kernel */ > + image->elf_headers_sz = kbuf.memsz; > + /* Record the index of the elfcorehdr segment */ > + image->elf_index = image->nr_segments; > + image->elf_index_valid = true; > +#else > kbuf.memsz = kbuf.bufsz; > +#endif > kbuf.buf_align = ELF_CORE_HEADER_ALIGN; > kbuf.mem = KEXEC_BUF_MEM_UNKNOWN; > ret = kexec_add_buffer(&kbuf); > @@ -413,3 +424,112 @@ int crash_load_segments(struct kimage *image) > return ret; > } > #endif /* CONFIG_KEXEC_FILE */ > + > +#ifdef CONFIG_CRASH_HOTPLUG > +static void *map_crash_pages(unsigned long paddr, unsigned long size) > +{ > + /* > + * NOTE: The addresses and sizes passed to this routine have > + * already been fully aligned on page boundaries. There is no > + * need for massaging the address or size. > + */ > + void *ptr = NULL; > + > + /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */ > + if (size > 0) { > + struct page *page = pfn_to_page(paddr >> PAGE_SHIFT); > + > + ptr = kmap(page); > + } > + > + return ptr; > +} > + > +static void unmap_crash_pages(void **ptr) > +{ > + if (ptr) { > + if (*ptr) > + kunmap(*ptr); > + *ptr = NULL; > + } > +} > + > +/** > + * arch_crash_hotplug_handler() - Handle hotplug elfcorehdr changes > + * @image: the active struct kimage > + * @hp_action: the hot un/plug action being handled > + * @a: first parameter dependent upon hp_action > + * @b: first parameter dependent upon hp_action > + * > + * To accurately reflect hot un/plug changes, the elfcorehdr (which > + * is passed to the crash kernel via the elfcorehdr= parameter) > + * must be updated with the new list of CPUs and memories. The new > + * elfcorehdr is prepared in a kernel buffer, and if no errors, ~~~~~~~~~~~~~~~~~~ can be removed. > + * then it is written on top of the existing/old elfcorehdr. > + * > + * For hotplug changes to elfcorehdr to work, two conditions are > + * needed: > + * First, the segment containing the elfcorehdr must be large enough > + * to permit a growing number of resources. See > + * CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ. > + * Second, purgatory must explicitly exclude the elfcorehdr from the > + * list of segments it checks (since the elfcorehdr changes and thus > + * would require an update to purgatory itself to update the digest). > + * > + */ > +void arch_crash_hotplug_handler(struct kimage *image, > + unsigned int hp_action, unsigned long a, unsigned long b) > +{ > + struct kexec_segment *ksegment; > + unsigned char *ptr = NULL; > + unsigned long elfsz = 0; > + void *elfbuf = NULL; > + unsigned long mem, memsz; > + > + /* Must have valid elfcorehdr index */ Redundant code comment can be removed. > + if (!image->elf_index_valid) { > + pr_err("crash hp: unable to locate elfcorehdr segment"); > + goto out; > + } > + > + ksegment = &image->segment[image->elf_index]; > + mem = ksegment->mem; > + memsz = ksegment->memsz; > + > + /* > + * Create the new elfcorehdr reflecting the changes to CPU and/or > + * memory resources. The elfcorehdr segment memsz must be > + * sufficiently large to accommodate increases due to hotplug > + * activity. See CRASH_HOTPLUG_ELFCOREHDR_SZ. > + */ This paragraph could be duplicated with the part in kernel-doc. Considering to drop one? > + if (prepare_elf_headers(image, &elfbuf, &elfsz)) { > + pr_err("crash hp: unable to prepare elfcore headers"); > + goto out; > + } > + if (elfsz > memsz) { > + pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu", > + elfsz, memsz); > + goto out; > + } > + > + /* > + * At this point, we are all but assured of success. > + * Copy new elfcorehdr into destination. > + */ > + ptr = map_crash_pages(mem, memsz); > + if (ptr) { > + /* Temporarily invalidate the crash image while it is replaced */ > + xchg(&kexec_crash_image, NULL); > + /* Write the new elfcorehdr into memory */ No need, the code is self explanatory. > + memcpy_flushcache((void *)ptr, elfbuf, elfsz); > + /* The crash image is now valid once again */ ditto. Sometime over commenting is not suggested. > + xchg(&kexec_crash_image, image); > + } > + unmap_crash_pages((void **)&ptr); > + pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem); > + > +out: > + if (elfbuf) > + vfree(elfbuf); > +} > +#endif /* CONFIG_CRASH_HOTPLUG */ > -- > 2.27.0 >