Messages in this thread | | | Date | Thu, 25 Aug 2022 14:42:30 -0500 | Subject | Re: [PATCH v10 8/8] x86/crash: Add x86 crash hotplug support | From | Eric DeVolder <> |
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Hi Baoquan, I've v11 ready to go, but I did raise some questions below which would be good to resolve before posting. Thanks! eric
On 8/16/22 10:23, Eric DeVolder wrote: > > > On 8/12/22 19:34, Baoquan He wrote: >> On 07/21/22 at 02:17pm, Eric DeVolder wrote: >> ...snip.... >>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >>> index e58798f636d4..bb59596c8bea 100644 >>> --- a/arch/x86/Kconfig >>> +++ b/arch/x86/Kconfig >>> @@ -2065,6 +2065,17 @@ 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 >> >> Do we need to enforce the value with page align and minimal size? I > > Are you asking about the value CRASH_MAX_MEMORY_RANGES? This value represents > the maximum number of memory ranges, and there Elf64_Phdrs, that we need to > allow for elfcorehdr memory. So I'm not sure what the concern for alignment > is. I suppose we could also institute a minimum size for this value, say 1024. > >> checked crash_load_segments() in arch/x86/kernel/crash.c, it does the >> page size aligning in kexec_add_buffer(). And in >> load_crashdump_segments() of >> kexec-tools/kexec/arch/i386/crashdump-x86.c, it creates elfcorehdr at >> below code, the align is 1024, and in generic add_buffer() >> implementation, it enforces the memsz page aligned, and changes the >> passed align as page alignment. >> >> >> elfcorehdr = add_buffer(info, tmp, bufsz, memsz, align, min_base, >> max_addr, -1); >> >> Maybe we should at least mention this in the help text to notice people. > > Unfortunately I do not yet understand the concern being raised. > >> >>> + 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/crash.h b/arch/x86/include/asm/crash.h >>> index 8b6bd63530dc..96051d8e4b45 100644 >>> --- a/arch/x86/include/asm/crash.h >>> +++ b/arch/x86/include/asm/crash.h >>> @@ -9,4 +9,24 @@ int crash_setup_memmap_entries(struct kimage *image, >>> struct boot_params *params); >>> void crash_smp_send_stop(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, unsigned int cpu); >>> +#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 >>> + >>> #endif /* _ASM_X86_CRASH_H */ >>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c >>> index 9ceb93c176a6..55dda4fcde6e 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 +398,17 @@ 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); >> >> Do we need to break the line to 80 chars? > > Sure, I will do so. > >> >>> + /* For marking as usable to crash kernel */ >>> + image->elf_headers_sz = kbuf.memsz; >> >> Do we need this code comment? > > Well, it did take me a while to figure this particular item out in order for all > this code to work right (else the crash kernel would fail at boot time). So I > think it best to keep this comment. > >> >>> + /* Record the index of the elfcorehdr segment */ >>> + image->elfcorehdr_index = image->nr_segments; >> >> And this place? > > Not necessarily needed, but I've found it useful. > >> >>> + 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 +423,107 @@ int crash_load_segments(struct kimage *image) >>> return ret; >>> } >>> #endif /* CONFIG_KEXEC_FILE */ >>> + >>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG) >>> +void *arch_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. >>> + */ >> >> Can we move the code comment above function interface? > > Yes > >> >>> + void *ptr = NULL; >>> + >>> + /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */ >> >> Do we need this code comment? On ARCH where proctionion is made, we >> surely need to the protect/unprotect. > > I will remove this; I've mentioned this in handle_hotplug_event() where these > protect/unprotect functions are called. > >> >>> + 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 >>> + * @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). >> >> Isn't this generic concept to crash hotplug? Should we move it out to >> some generic place? > > Yes, so I will relocate this. > >> >>> + * >>> + */ >>> +void arch_crash_handle_hotplug_event(struct kimage *image, >>> + unsigned int hp_action, unsigned int cpu) >> >> The passed in 'cpu' is not used at all, what is it added for? I didn't >> see explanation about it. > > Well its not used for x86, but as I recall, Sourabh Jain needed it for the PowerPC handler. > >> >>> +{ >>> + 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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