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@xxxxxxxxxx> --- 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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