Messages in this thread | | | Date | Wed, 25 May 2022 08:51:55 -0500 | Subject | Re: [PATCH v8 6/7] x86/crash: Add x86 crash hotplug support for kexec_file_load | From | Eric DeVolder <> |
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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 <eric.devolder@oracle.com> >> --- >> 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 <linux/slab.h> >> #include <linux/vmalloc.h> >> #include <linux/memblock.h> >> +#include <linux/highmem.h> >> #include <asm/processor.h> >> #include <asm/hardirq.h> >> @@ -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 >
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