Messages in this thread | | | Date | Fri, 1 Apr 2022 13:34:33 -0500 | Subject | Re: [PATCH v5 7/8] x86/crash: Add x86 crash hotplug support for kexec_file_load | From | Eric DeVolder <> |
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On 3/31/22 05:34, Baoquan He wrote: > On 03/03/22 at 11:27am, 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 if no errors occur, it is >> installed over the top of the existing elfcorehdr. >> >> In the patch 'crash hp: 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_HOTPLUG_ELFCOREHDR_SZ configure item. >> >> With this change, the kexec_file_load syscall (not kexec_load) >> is supported. When loading the crash kernel via kexec_file_load, >> the elfcorehdr is identified at load time in crash_load_segments(). > > I tune the log a little, please check: > > [PATCH v5 7/8] x86/crash: Add x86 crash hotplug support for kexec_file_load > > 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 need be > generated from the available CPUs and memory. The new elfcorehdr > is prepared into a buffer, 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_HOTPLUG_ELFCOREHDR_SZ configure item. > > With this change, crash hotplug for kexec_file_load syscall > is supported. When loading kdump kernel via kexec_file_load, > the elfcorehdr is identified at load time in crash_load_segments(). > Updated the commit message.
>> > >> >> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com> >> --- >> arch/x86/kernel/crash.c | 120 ++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 120 insertions(+) >> >> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c >> index 9db41cce8d97..5da30e2bc780 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; >> >> +#ifdef CONFIG_CRASH_HOTPLUG >> + /* Ensure elfcorehdr segment large enough for hotplug changes */ >> + kbuf.memsz = CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ; >> + /* For marking as usable to crash kernel */ >> + image->elf_headers_sz = kbuf.memsz; >> + /* Record the index of the elfcorehdr segment */ >> + image->elf_index = image->nr_segments; >> + image->elf_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 +424,112 @@ int crash_load_segments(struct kimage *image) >> return ret; >> } >> #endif /* CONFIG_KEXEC_FILE */ >> + >> +#ifdef CONFIG_CRASH_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_hotplug_handler() - Handle hotplug elfcorehdr changes >> + * @image: the active struct kimage >> + * @hp_action: the hot un/plug action being handled >> + * @a: first parameter dependent upon hp_action >> + * @b: first parameter dependent upon hp_action >> + * >> + * 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 if no errors, > ~~~~~~~~~~~~~~~~~~ > can be removed. done
>> + * 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 >> + * CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ. >> + * 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_hotplug_handler(struct kimage *image, >> + unsigned int hp_action, unsigned long a, unsigned long b) >> +{ >> + struct kexec_segment *ksegment; >> + unsigned char *ptr = NULL; >> + unsigned long elfsz = 0; >> + void *elfbuf = NULL; >> + unsigned long mem, memsz; >> + >> + /* Must have valid elfcorehdr index */ > Redundant code comment can be removed. done
> >> + if (!image->elf_index_valid) { >> + pr_err("crash hp: unable to locate elfcorehdr segment"); >> + goto out; >> + } >> + >> + ksegment = &image->segment[image->elf_index]; >> + mem = ksegment->mem; >> + memsz = ksegment->memsz; >> + >> + /* >> + * Create the new elfcorehdr reflecting the changes to CPU and/or >> + * memory resources. The elfcorehdr segment memsz must be >> + * sufficiently large to accommodate increases due to hotplug >> + * activity. See CRASH_HOTPLUG_ELFCOREHDR_SZ. >> + */ > This paragraph could be duplicated with the part in kernel-doc. > Considering to drop one? done
>> + if (prepare_elf_headers(image, &elfbuf, &elfsz)) { >> + pr_err("crash hp: unable to prepare elfcore headers"); >> + goto out; >> + } >> + if (elfsz > memsz) { >> + pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu", >> + elfsz, memsz); >> + goto out; >> + } >> + >> + /* >> + * At this point, we are all but assured of success. >> + * Copy new elfcorehdr into destination. >> + */ >> + ptr = map_crash_pages(mem, memsz); >> + if (ptr) { >> + /* Temporarily invalidate the crash image while it is replaced */ >> + xchg(&kexec_crash_image, NULL); >> + /* Write the new elfcorehdr into memory */ > No need, the code is self explanatory. done
>> + memcpy_flushcache((void *)ptr, elfbuf, elfsz); >> + /* The crash image is now valid once again */ > > ditto. Sometime over commenting is not suggested. done
> >> + xchg(&kexec_crash_image, image); >> + } >> + unmap_crash_pages((void **)&ptr); >> + pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem); >> + >> +out: >> + if (elfbuf) >> + vfree(elfbuf); >> +} >> +#endif /* CONFIG_CRASH_HOTPLUG */ >> -- >> 2.27.0 >> >
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