Messages in this thread | | | Date | Mon, 17 Oct 2022 12:24:39 +0530 | Subject | Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support | From | Sourabh Jain <> |
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On 08/10/22 01:03, Eric DeVolder wrote: > > > On 9/19/22 02:06, Sourabh Jain wrote: >> >> On 10/09/22 02:35, 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> >>> Acked-by: Baoquan He <bhe@redhat.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 >>> + >>> #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; >> >> On PowerPC, while preparing the elf core header the memblock >> structure is used to prepare program header for memory regions of >> elfcorehdr. Since the above arch specific hotplug handler gets >> invoked when memory is marked offline (MEM_OFFLINE) which is before >> memblock structure gets updated so on PowerPC the above handler may >> not work for memory hotplug case. >> >> Just wondering which data structure is used to get the list of memory >> regions while preparing program header for memory regions of >> elfcorehdr on other architectures? >> >> Thanks, >> Sourabh Jain > > I think your request to report the memory block address in comments of > patch 3/7 "crash: add generic infrastructure" cover this scenario now. Yes, the asked changes will make easy for PowerPC to recreate elfcorehdr.
Thanks, Sourabh Jain
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