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Fri, 26 Aug 2022 00:35:24 -0400 X-MC-Unique: 921cXJffMYabm40UmuGCGQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id F1BD98032F6; Fri, 26 Aug 2022 04:35:23 +0000 (UTC) Received: from localhost (ovpn-13-127.pek2.redhat.com [10.72.13.127]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B62E6945DD; Fri, 26 Aug 2022 04:35:22 +0000 (UTC) Date: Fri, 26 Aug 2022 12:35:18 +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 v10 8/8] x86/crash: Add x86 crash hotplug support Message-ID: References: <20220721181747.1640-1-eric.devolder@oracle.com> <20220721181747.1640-9-eric.devolder@oracle.com> <0395a745-edbb-275a-f37f-c6e799388da1@oracle.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0395a745-edbb-275a-f37f-c6e799388da1@oracle.com> X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220825_213533_579480_03678265 X-CRM114-Status: GOOD ( 48.38 ) 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 08/16/22 at 10:23am, Eric DeVolder wrote: > > > On 8/12/22 19:34, Baoquan He wrote: > > On 07/21/22 at 02:17pm, Eric DeVolder wrote: > > ...snip.... > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > > index e58798f636d4..bb59596c8bea 100644 > > > --- a/arch/x86/Kconfig > > > +++ b/arch/x86/Kconfig > > > @@ -2065,6 +2065,17 @@ config CRASH_DUMP > > > (CONFIG_RELOCATABLE=y). > > > For more details see Documentation/admin-guide/kdump/kdump.rst > > > +config CRASH_MAX_MEMORY_RANGES > > > + depends on CRASH_DUMP && KEXEC_FILE && (HOTPLUG_CPU || MEMORY_HOTPLUG) > > > + int > > > + default 32768 > > > > Do we need to enforce the value with page align and minimal size? I > > Are you asking about the value CRASH_MAX_MEMORY_RANGES? This value represents > the maximum number of memory ranges, and there Elf64_Phdrs, that we need to > allow for elfcorehdr memory. So I'm not sure what the concern for alignment > is. I suppose we could also institute a minimum size for this value, say 1024. > > > checked crash_load_segments() in arch/x86/kernel/crash.c, it does the > > page size aligning in kexec_add_buffer(). And in > > load_crashdump_segments() of > > kexec-tools/kexec/arch/i386/crashdump-x86.c, it creates elfcorehdr at > > below code, the align is 1024, and in generic add_buffer() > > implementation, it enforces the memsz page aligned, and changes the > > passed align as page alignment. > > > > > > elfcorehdr = add_buffer(info, tmp, bufsz, memsz, align, min_base, > > max_addr, -1); > > > > Maybe we should at least mention this in the help text to notice people. > > Unfortunately I do not yet understand the concern being raised. Oops, never mind, I misunderstood CRASH_MAX_MEMORY_RANGES. Thought it's the range vlaue of buffer containing elfcorehdr, I must be dizzy when reading this part. > > > ...snip... > > > diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c > > > index 9ceb93c176a6..55dda4fcde6e 100644 > > > --- a/arch/x86/kernel/crash.c > > > +++ b/arch/x86/kernel/crash.c > > > @@ -25,6 +25,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > #include > > > #include > > > @@ -397,7 +398,17 @@ int crash_load_segments(struct kimage *image) > > > image->elf_headers = kbuf.buffer; > > > image->elf_headers_sz = kbuf.bufsz; > > > +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG) > > > + /* Ensure elfcorehdr segment large enough for hotplug changes */ > > > + kbuf.memsz = (CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES) * sizeof(Elf64_Phdr); > > > > Do we need to break the line to 80 chars? > > Sure, I will do so. > > > > > > + /* For marking as usable to crash kernel */ > > > + image->elf_headers_sz = kbuf.memsz; > > > > Do we need this code comment? > > Well, it did take me a while to figure this particular item out in order for all > this code to work right (else the crash kernel would fail at boot time). So I > think it best to keep this comment. > > > > > > + /* Record the index of the elfcorehdr segment */ > > > + image->elfcorehdr_index = image->nr_segments; > > > > And this place? > > Not necessarily needed, but I've found it useful. > > > > > > + image->elfcorehdr_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); > > > @@ -412,3 +423,107 @@ int crash_load_segments(struct kimage *image) > > > return ret; > > > } > > > #endif /* CONFIG_KEXEC_FILE */ > > > + > > > +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG) > > > +void *arch_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. > > > + */ > > > > Can we move the code comment above function interface? > > Yes > > > > > > + void *ptr = NULL; > > > + > > > + /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */ > > > > Do we need this code comment? On ARCH where proctionion is made, we > > surely need to the protect/unprotect. > > I will remove this; I've mentioned this in handle_hotplug_event() where these > protect/unprotect functions are called. > > > > > > + if (size > 0) { > > > + struct page *page = pfn_to_page(paddr >> PAGE_SHIFT); > > > + > > > + ptr = kmap_local_page(page); > > > + } > > > + > > > + return ptr; > > > +} > > > + > > > +void arch_unmap_crash_pages(void **ptr) > > > +{ > > > + if (ptr) { > > > + if (*ptr) > > > + kunmap_local(*ptr); > > > + *ptr = NULL; > > > + } > > > +} > > > + > > > +/** > > > + * arch_crash_handle_hotplug_event() - Handle hotplug elfcorehdr changes > > > + * @image: the active struct kimage > > > + * @hp_action: the hot un/plug action being handled > > > + * @cpu: when KEXEC_CRASH_HP_ADD/REMOVE_CPU, the cpu affected > > > + * > > > + * 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 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 the > > > + * CONFIG_CRASH_MAX_MEMORY_RANGES description. > > > + * 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). > > > > Isn't this generic concept to crash hotplug? Should we move it out to > > some generic place? > > Yes, so I will relocate this. > > > > > > + * > > > + */ > > > +void arch_crash_handle_hotplug_event(struct kimage *image, > > > + unsigned int hp_action, unsigned int cpu) > > > > The passed in 'cpu' is not used at all, what is it added for? I didn't > > see explanation about it. > > Well its not used for x86, but as I recall, Sourabh Jain needed it for the PowerPC handler. Then better mention this in log or add code comment, otherwise confusion could be caused. _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec