Messages in this thread | | | Date | Tue, 6 Sep 2022 10:37:06 -0500 | Subject | Re: [PATCH v11 7/7] x86/crash: Add x86 crash hotplug support | From | Eric DeVolder <> |
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On 9/4/22 22:19, Baoquan He wrote: > On 08/26/22 at 01:37pm, 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. >> >> When loading the crash kernel via kexec_load or kexec_file_load, >> the elfcorehdr is identified at run time in >> crash_core:handle_hotplug_event(). >> >> 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. The kexec_load is also supported, but also >> requires a corresponding change to userspace kexec-tools. >> >> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com> >> --- >> arch/x86/Kconfig | 11 ++++ >> arch/x86/include/asm/kexec.h | 20 +++++++ >> arch/x86/kernel/crash.c | 102 +++++++++++++++++++++++++++++++++++ >> 3 files changed, 133 insertions(+) >> >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >> index f9920f1341c8..cdfc9b2fdf98 100644 >> --- a/arch/x86/Kconfig >> +++ b/arch/x86/Kconfig >> @@ -2056,6 +2056,17 @@ 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/include/asm/kexec.h b/arch/x86/include/asm/kexec.h >> index a3760ca796aa..432073385b2d 100644 >> --- a/arch/x86/include/asm/kexec.h >> +++ b/arch/x86/include/asm/kexec.h >> @@ -212,6 +212,26 @@ typedef void crash_vmclear_fn(void); >> extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss; >> extern void kdump_nmi_shootdown_cpus(void); >> >> +void *arch_map_crash_pages(unsigned long paddr, unsigned long size); >> +#define arch_map_crash_pages arch_map_crash_pages >> + >> +void arch_unmap_crash_pages(void **ptr); >> +#define arch_unmap_crash_pages arch_unmap_crash_pages >> + >> +void arch_crash_handle_hotplug_event(struct kimage *image, >> + unsigned int hp_action); >> +#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event >> + >> +#ifdef CONFIG_HOTPLUG_CPU >> +static inline int crash_hotplug_cpu_support(void) { return 1; } >> +#define crash_hotplug_cpu_support crash_hotplug_cpu_support >> +#endif >> + >> +#ifdef CONFIG_MEMORY_HOTPLUG >> +static inline int crash_hotplug_memory_support(void) { return 1; } >> +#define crash_hotplug_memory_support crash_hotplug_memory_support >> +#endif > > Check these two functions again, wonder whether this is a common usage > to show support of a feature. I don't remember where we do like this. We > usually define a global variable to mark it? Anyway, it works. See if > other people have comments, I could be ignorant.
These functions are for use in generating the value of the associated the sysfs attribute.
The default-value function (which previously was a __weak function) is in include/linux/kexec.h and the arch-specific override in arch/<arch>/include/asm/kexec.h. This default-value function sets the return to 0, for not supported.
I looked around a bit, and don't necessarily see a precedent. Then again some of this conversion of away from __weak is still making its way. I did briefly experiment with using a variable but decided there would still need to be a similar function needed (mostly likely on the subsys_initcall) in order to properly set the variable. So with the move away from __weak, it seemed to make sense to just keep the individual functions as they are now, in the spirit of the move away from __weak.
If the variable is still desired, please let me know. I'll post v12 at the end of the week to incorporate the fixes for some of the nits previously identified!
> > Other than this tiny concern, this patch looks good to me: > > Acked-by: Baoquan He <bhe@redhat.com>
Thank you! eric
> >> + >> #endif /* __ASSEMBLY__ */ >> >> #endif /* _ASM_X86_KEXEC_H */ >> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c >> index 9ceb93c176a6..8fc7d678ac72 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> >> @@ -397,7 +398,18 @@ 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); >> + /* Mark as usable to crash kernel, else crash kernel fails on boot */ >> + image->elf_headers_sz = kbuf.memsz; >> + 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); >> @@ -412,3 +424,93 @@ int crash_load_segments(struct kimage *image) >> return ret; >> } >> #endif /* CONFIG_KEXEC_FILE */ >> + >> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG) >> +/* >> + * 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 *arch_map_crash_pages(unsigned long paddr, unsigned long size) >> +{ >> + void *ptr = NULL; >> + >> + 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 >> + * >> + * To accurately reflect hot un/plug changes, the new elfcorehdr >> + * is prepared in a kernel buffer, and then it is written on top >> + * of the existing/old elfcorehdr. >> + */ >> +void arch_crash_handle_hotplug_event(struct kimage *image, >> + unsigned int hp_action) >> +{ >> + struct kexec_segment *ksegment; >> + unsigned char *ptr = NULL; >> + unsigned long elfsz = 0; >> + void *elfbuf = NULL; >> + unsigned long mem, memsz; >> + >> + /* >> + * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event() >> + */ >> + 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; >> + } >> + 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 = arch_map_crash_pages(mem, memsz); >> + if (ptr) { >> + /* >> + * Temporarily invalidate the crash image while the >> + * elfcorehdr is updated. >> + */ >> + xchg(&kexec_crash_image, NULL); >> + memcpy_flushcache((void *)ptr, elfbuf, elfsz); >> + xchg(&kexec_crash_image, image); >> + } >> + arch_unmap_crash_pages((void **)&ptr); >> + pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem); >> + >> +out: >> + if (elfbuf) >> + vfree(elfbuf); >> +} >> +#endif >> -- >> 2.31.1 >> >
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