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Wed, 25 May 2022 05:26:04 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B602152051; Wed, 25 May 2022 05:26:04 +0000 (GMT) Received: from [9.43.97.219] (unknown [9.43.97.219]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id AA4FC5204E; Wed, 25 May 2022 05:25:59 +0000 (GMT) Message-ID: <60bd09e4-91d6-d81c-3b97-1d5334efe6e7@linux.ibm.com> Date: Wed, 25 May 2022 10:55:58 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v8 6/7] x86/crash: Add x86 crash hotplug support for kexec_file_load Content-Language: en-US To: Eric DeVolder , linux-kernel@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com Cc: 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 References: <20220505184603.1548-1-eric.devolder@oracle.com> <20220505184603.1548-7-eric.devolder@oracle.com> From: Sourabh Jain In-Reply-To: <20220505184603.1548-7-eric.devolder@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: ExG6Tf-04b6aLsrpIR4HSwUv1IbKn9PG X-Proofpoint-GUID: zwaqoCIM07dz8UgEro0IhQgnQoCeqHIV X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-25_01,2022-05-23_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 bulkscore=0 phishscore=0 lowpriorityscore=0 impostorscore=0 clxscore=1015 mlxlogscore=999 malwarescore=0 suspectscore=0 mlxscore=0 adultscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2204290000 definitions=main-2205250027 X-Spam-Status: No, score=-5.3 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE, SPF_PASS,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 Hello Eric, On 06/05/22 00:16, 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 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_MAX_MEMORY_RANGES configure item. > > With this change, crash hotplug for kexec_file_load syscall > is supported. When loading the crash kernel via kexec_file_load, > the elfcorehdr is identified at load time in crash_load_segments(). > > Signed-off-by: Eric DeVolder > --- > arch/x86/Kconfig | 11 ++++ > arch/x86/kernel/crash.c | 117 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 128 insertions(+) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 4bed3abf444d..bf1201fe6981 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -2072,6 +2072,17 @@ 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 > + help > + For the kexec_file_load path, specify the maximum number of > + memory regions, eg. as represented by the 'System RAM' entries > + in /proc/iomem, that the elfcorehdr buffer/segment can accommodate. > + This value is combined with NR_CPUS and multiplied by Elf64_Phdr > + size to determine the final buffer size. > + > config KEXEC_JUMP > bool "kexec jump" > depends on KEXEC && HIBERNATION > diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c > index 9db41cce8d97..951ef365f0a7 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; > > +#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); > + /* For marking as usable to crash kernel */ > + image->elf_headers_sz = kbuf.memsz; > + /* Record the index of the elfcorehdr segment */ > + image->elfcorehdr_index = image->nr_segments; > + 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); > @@ -413,3 +424,109 @@ int crash_load_segments(struct kimage *image) > return ret; > } > #endif /* CONFIG_KEXEC_FILE */ > + > +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_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_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). > + * > + */ > +void arch_crash_handle_hotplug_event(struct kimage *image, > + unsigned int hp_action, unsigned int cpu) > +{ > + struct kexec_segment *ksegment; > + unsigned char *ptr = NULL; > + unsigned long elfsz = 0; > + void *elfbuf = NULL; > + unsigned long mem, memsz; > + > + if (!image->elfcorehdr_index_valid) { > + pr_err("crash hp: unable to locate elfcorehdr segment"); > + goto out; > + } > + > + ksegment = &image->segment[image->elfcorehdr_index]; > + mem = ksegment->mem; > + memsz = ksegment->memsz; > + > + /* > + * Create the new elfcorehdr reflecting the changes to CPU and/or > + * memory resources. > + */ > + if (prepare_elf_headers(image, &elfbuf, &elfsz)) { > + pr_err("crash hp: unable to prepare elfcore headers"); > + goto out; Prepare_elf_header uses crash_prepare_elf64_headers function to generate elfcorehdr. Since crash_prepare_elf64_headers is defined under CONFIG_KEXEC_FILE option we will have build issues if CONFIG_KEXEC is enabled and CONFIG_KEXEC_FILE is disabled. How about moving crash_prepare_elf64_headers function to kernel/kexec_core.c? Thanks, Sourabh Jain