From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric DeVolder Date: Wed, 25 May 2022 08:51:55 -0500 Subject: [PATCH v8 6/7] x86/crash: Add x86 crash hotplug support for kexec_file_load In-Reply-To: <60bd09e4-91d6-d81c-3b97-1d5334efe6e7@linux.ibm.com> References: <20220505184603.1548-1-eric.devolder@oracle.com> <20220505184603.1548-7-eric.devolder@oracle.com> <60bd09e4-91d6-d81c-3b97-1d5334efe6e7@linux.ibm.com> Message-ID: <526d44b2-0120-2d52-aac3-57155a2bf80b@oracle.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kexec@lists.infradead.org On 5/25/22 00:25, Sourabh Jain wrote: > 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? Yes, of course. I originally protected against this scenario with having the CRASH_HOTPLUG dependent on KEXEC_FILE, but as we eliminated CRASH_HOTPLUG, your suggestion above is on point. Thanks! eric > > Thanks, > Sourabh Jain >