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Tue, 14 Mar 2023 06:43:30 -0400 X-MC-Unique: EAvHKNpsN9CxgMptaQqMfg-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D2D062810C08; Tue, 14 Mar 2023 10:43:28 +0000 (UTC) Received: from localhost (ovpn-12-81.pek2.redhat.com [10.72.12.81]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AFBE9400F55; Tue, 14 Mar 2023 10:43:27 +0000 (UTC) Date: Tue, 14 Mar 2023 18:43:24 +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 v19 2/7] crash: add generic infrastructure for crash hotplug support Message-ID: References: <20230306162228.8277-1-eric.devolder@oracle.com> <20230306162228.8277-3-eric.devolder@oracle.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230306162228.8277-3-eric.devolder@oracle.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230314_034338_465430_7DCB2E76 X-CRM114-Status: GOOD ( 32.83 ) 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 03/06/23 at 11:22am, Eric DeVolder wrote: ...... > +#ifdef CONFIG_CRASH_HOTPLUG > +#undef pr_fmt > +#define pr_fmt(fmt) "crash hp: " fmt > +/* > + * To accurately reflect hot un/plug changes of cpu and memory resources > + * (including onling and offlining of those resources), the elfcorehdr > + * (which is passed to the crash kernel via the elfcorehdr= parameter) > + * must be updated with the new list of CPUs and memories. > + * > + * In order to make changes to elfcorehdr, two conditions are needed: > + * First, the segment containing the elfcorehdr must be large enough > + * to permit a growing number of resources; the elfcorehdr memory size > + * is based on NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. > + * 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). > + */ > +static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu) > +{ > + /* Obtain lock while changing crash information */ > + if (kexec_trylock()) { > + > + /* Check kdump is loaded */ > + if (kexec_crash_image) { If the above check failed, I would directly return or jump out becuase one indentation can be reduced. > + struct kimage *image = kexec_crash_image; > + > + if (hp_action == KEXEC_CRASH_HP_ADD_CPU || > + hp_action == KEXEC_CRASH_HP_REMOVE_CPU) > + pr_debug("hp_action %u, cpu %u\n", hp_action, cpu); > + else > + pr_debug("hp_action %u\n", hp_action); > + > + /* > + * When the struct kimage is allocated, the elfcorehdr_index > + * is set to -1. Find the segment containing the elfcorehdr, > + * if not already found. This works for both the kexec_load > + * and kexec_file_load paths. > + */ > + if (image->elfcorehdr_index < 0) { > + unsigned long mem; > + unsigned char *ptr; > + unsigned int n; > + > + for (n = 0; n < image->nr_segments; n++) { > + mem = image->segment[n].mem; > + ptr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT)); > + if (ptr) { > + /* The segment containing elfcorehdr */ > + if (memcmp(ptr, ELFMAG, SELFMAG) == 0) { > + image->elfcorehdr_index = (int)n; > + } > + kunmap_local(ptr); > + } > + } > + } > + > + if (image->elfcorehdr_index < 0) { > + pr_err("unable to locate elfcorehdr segment"); > + goto out; > + } > + > + /* Needed in order for the segments to be updated */ > + arch_kexec_unprotect_crashkres(); > + > + /* Differentiate between normal load and hotplug update */ > + image->hp_action = hp_action; > + > + /* Now invoke arch-specific update handler */ > + arch_crash_handle_hotplug_event(image); > + > + /* No longer handling a hotplug event */ > + image->hp_action = KEXEC_CRASH_HP_NONE; > + image->elfcorehdr_updated = true; > + > + /* Change back to read-only */ > + arch_kexec_protect_crashkres(); > + } > + > +out: > + /* Release lock now that update complete */ > + kexec_unlock(); > + } > +} > + > +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v) > +{ > + switch (val) { > + case MEM_ONLINE: > + crash_handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, > + KEXEC_CRASH_HP_INVALID_CPU); > + break; > + > + case MEM_OFFLINE: > + crash_handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, > + KEXEC_CRASH_HP_INVALID_CPU); > + break; > + } > + return NOTIFY_OK; > +} > + > +static struct notifier_block crash_memhp_nb = { > + .notifier_call = crash_memhp_notifier, > + .priority = 0 > +}; > + Because for_each_possible_cpu() is taken in crash_prepare_elf64_headers(), x86 doesn't need to respond to cpu hotplug or doesn't do anything with this patchset. This cpu part in infrastructure is only for the later powerpc usage, right? > +static int crash_cpuhp_online(unsigned int cpu) > +{ > + crash_handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu); > + return 0; > +} > + > +static int crash_cpuhp_offline(unsigned int cpu) > +{ > + crash_handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu); > + return 0; > +} > + > +static int __init crash_hotplug_init(void) > +{ > + int result = 0; > + > + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) > + register_memory_notifier(&crash_memhp_nb); > + > + if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) { > + result = cpuhp_setup_state_nocalls(CPUHP_BP_PREPARE_DYN, > + "crash/cpuhp", crash_cpuhp_online, crash_cpuhp_offline); > + } > + > + return result; > +} > + > +subsys_initcall(crash_hotplug_init); > +#endif > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index 969e8f52f7da..f2f9d41ce5df 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -276,6 +276,11 @@ struct kimage *do_kimage_alloc_init(void) > /* Initialize the list of unusable pages */ > INIT_LIST_HEAD(&image->unusable_pages); > > +#ifdef CONFIG_CRASH_HOTPLUG > + image->elfcorehdr_index = -1; > + image->elfcorehdr_updated = false; > +#endif > + > return image; > } > > -- > 2.31.1 > _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec