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Is that > solved? In looking at David's comments on v8: - [PATCH v8 2/7] crash: prototype change for crash_prepare_elf64_headers I adjusted per feedback and responded as such. He provided an Acked-by. - [PATCH v8 3/7] crash: add generic infrastructure for crash hotplug support He says do not use WARN* on expected error paths. I instead used WARN_ONCE(), but I didn't consider this an error path. Nonetheless, I'll remove the message altogether in v11. - [PATCH v8 0/7] crash: Kernel handling of CPU and memory hot un/plug David muses about a better name, but that was in response to Sourabh's and I exchange on the sysfs attributes to use to report the presence of this feature. In the end, I used something altogether different, as presented in v10 (and the corresponding udev solution/change that goes hand in hand with it). Let me know if I've missed anything else? Sourabh points out a build problem for architectures without this feature support, so a v11 is warranted. But I'll wait to post that until I hear that I've addressed the previous questions. Thanks, eric > >> >> On 6/13/22 17:42, Eric DeVolder wrote: >>> When the kdump service is loaded, if a CPU or memory is hot >>> un/plugged, the crash elfcorehdr (for x86), which describes the CPUs >>> and memory in the system, must also be updated, else the resulting >>> vmcore is inaccurate (eg. missing either CPU context or memory >>> regions). >>> >>> The current solution utilizes udev to initiate an unload-then-reload >>> of the kdump image (e. kernel, initrd, boot_params, puratory and >>> elfcorehdr) by the userspace kexec utility. In previous posts I have >>> outlined the significant performance problems related to offloading >>> this activity to userspace. >>> >>> This patchset introduces a generic crash hot un/plug handler that >>> registers with the CPU and memory notifiers. Upon CPU or memory >>> changes, this generic handler is invoked and performs important >>> housekeeping, for example obtaining the appropriate lock, and then >>> invokes an architecture specific handler to do the appropriate >>> updates. >>> >>> In the case of x86_64, the arch specific handler generates a new >>> elfcorehdr, and overwrites the old one in memory. No involvement >>> with userspace needed. >>> >>> To realize the benefits/test this patchset, one must make a couple >>> of minor changes to userspace: >>> >>> - Prevent udev from updating kdump crash kernel on hot un/plug changes. >>> Add the following as the first lines to the udev rule file >>> /usr/lib/udev/rules.d/98-kexec.rules: >>> >>> # The kernel handles updates to crash elfcorehdr for cpu and memory changes >>> SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" >>> SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" >>> >>> These lines will cause cpu and memory hot un/plug events to be >>> skipped within this rule file, if the kernel has these changes >>> enabled. >>> >>> - Change to the kexec_file_load for loading the kdump kernel: >>> Eg. on RHEL: in /usr/bin/kdumpctl, change to: >>> standard_kexec_args="-p -d -s" >>> which adds the -s to select kexec_file_load syscall. >>> >>> This patchset supports kexec_load with a modified kexec userspace >>> utility, and a working changeset to the kexec userspace utility >>> is provided here (and to use, the above change to standard_kexec_args >>> would be, for example, to append --hotplug instead of -s). >>> >>> diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c >>> index 9826f6d..4ed395a 100644 >>> --- a/kexec/arch/i386/crashdump-x86.c >>> +++ b/kexec/arch/i386/crashdump-x86.c >>> @@ -48,6 +48,7 @@ >>> #include >>> extern struct arch_options_t arch_options; >>> +extern int do_hotplug; >>> static int get_kernel_page_offset(struct kexec_info *UNUSED(info), >>> struct crash_elf_info *elf_info) >>> @@ -975,6 +976,14 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline, >>> } else { >>> memsz = bufsz; >>> } >>> + >>> + /* If hotplug support enabled, use larger size to accomodate changes */ >>> + if (do_hotplug) { >>> + long int nr_cpus = get_nr_cpus(); >>> + memsz = (nr_cpus + CRASH_MAX_MEMORY_RANGES) * sizeof(Elf64_Phdr); >>> + } >>> + >>> + info->elfcorehdr = >>> elfcorehdr = add_buffer(info, tmp, bufsz, memsz, align, min_base, >>> max_addr, -1); >>> dbgprintf("Created elf header segment at 0x%lx\n", elfcorehdr); >>> diff --git a/kexec/crashdump-elf.c b/kexec/crashdump-elf.c >>> index b8bb686..5e29f7a 100644 >>> --- a/kexec/crashdump-elf.c >>> +++ b/kexec/crashdump-elf.c >>> @@ -43,11 +43,7 @@ int FUNC(struct kexec_info *info, >>> int (*get_note_info)(int cpu, uint64_t *addr, uint64_t *len); >>> long int count_cpu; >>> - if (xen_present()) >>> - nr_cpus = xen_get_nr_phys_cpus(); >>> - else >>> - nr_cpus = sysconf(_SC_NPROCESSORS_CONF); >>> - >>> + nr_cpus = get_nr_cpus(); >>> if (nr_cpus < 0) { >>> return -1; >>> } >>> diff --git a/kexec/crashdump.h b/kexec/crashdump.h >>> index 18bd691..28d3278 100644 >>> --- a/kexec/crashdump.h >>> +++ b/kexec/crashdump.h >>> @@ -57,7 +57,6 @@ unsigned long phys_to_virt(struct crash_elf_info *elf_info, >>> unsigned long long paddr); >>> unsigned long xen_architecture(struct crash_elf_info *elf_info); >>> -int xen_get_nr_phys_cpus(void); >>> int xen_get_note(int cpu, uint64_t *addr, uint64_t *len); >>> int xen_get_crashkernel_region(uint64_t *start, uint64_t *end); >>> diff --git a/kexec/kexec-xen.h b/kexec/kexec-xen.h >>> index 70fb576..f54a2dd 100644 >>> --- a/kexec/kexec-xen.h >>> +++ b/kexec/kexec-xen.h >>> @@ -83,5 +83,6 @@ extern int __xc_interface_close(xc_interface *xch); >>> #endif >>> int xen_get_kexec_range(int range, uint64_t *start, uint64_t *end); >>> +int xen_get_nr_phys_cpus(void); >>> #endif /* KEXEC_XEN_H */ >>> diff --git a/kexec/kexec.c b/kexec/kexec.c >>> index 829a6ea..3668b73 100644 >>> --- a/kexec/kexec.c >>> +++ b/kexec/kexec.c >>> @@ -58,6 +58,7 @@ >>> unsigned long long mem_min = 0; >>> unsigned long long mem_max = ULONG_MAX; >>> +int do_hotplug = 0; >>> static unsigned long kexec_flags = 0; >>> /* Flags for kexec file (fd) based syscall */ >>> static unsigned long kexec_file_flags = 0; >>> @@ -489,6 +490,17 @@ static int add_backup_segments(struct kexec_info *info, >>> return 0; >>> } >>> +long int get_nr_cpus(void) >>> +{ >>> + long int nr_cpus; >>> + >>> + if (xen_present()) >>> + nr_cpus = xen_get_nr_phys_cpus(); >>> + else >>> + nr_cpus = sysconf(_SC_NPROCESSORS_CONF); >>> + return nr_cpus; >>> +} >>> + >>> static char *slurp_fd(int fd, const char *filename, off_t size, off_t *nread) >>> { >>> char *buf; >>> @@ -672,6 +684,14 @@ static void update_purgatory(struct kexec_info *info) >>> if (info->segment[i].mem == (void *)info->rhdr.rel_addr) { >>> continue; >>> } >>> + >>> + /* Don't include elfcorehdr in the checksum, if hotplug >>> + * support enabled. >>> + */ >>> + if (do_hotplug && (info->segment[i].mem == (void *)info->elfcorehdr)) { >>> + continue; >>> + } >>> + >>> sha256_update(&ctx, info->segment[i].buf, >>> info->segment[i].bufsz); >>> nullsz = info->segment[i].memsz - info->segment[i].bufsz; >>> @@ -1565,6 +1585,9 @@ int main(int argc, char *argv[]) >>> case OPT_PRINT_CKR_SIZE: >>> print_crashkernel_region_size(); >>> return 0; >>> + case OPT_HOTPLUG: >>> + do_hotplug = 1; >>> + break; >>> default: >>> break; >>> } >>> diff --git a/kexec/kexec.h b/kexec/kexec.h >>> index 0f97a97..b0428cc 100644 >>> --- a/kexec/kexec.h >>> +++ b/kexec/kexec.h >>> @@ -169,6 +169,7 @@ struct kexec_info { >>> int command_line_len; >>> int skip_checks; >>> + unsigned long elfcorehdr; >>> }; >>> struct arch_map_entry { >>> @@ -231,7 +232,8 @@ extern int file_types; >>> #define OPT_PRINT_CKR_SIZE 262 >>> #define OPT_LOAD_LIVE_UPDATE 263 >>> #define OPT_EXEC_LIVE_UPDATE 264 >>> -#define OPT_MAX 265 >>> +#define OPT_HOTPLUG 265 >>> +#define OPT_MAX 266 >>> #define KEXEC_OPTIONS \ >>> { "help", 0, 0, OPT_HELP }, \ >>> { "version", 0, 0, OPT_VERSION }, \ >>> @@ -258,6 +260,7 @@ extern int file_types; >>> { "debug", 0, 0, OPT_DEBUG }, \ >>> { "status", 0, 0, OPT_STATUS }, \ >>> { "print-ckr-size", 0, 0, OPT_PRINT_CKR_SIZE }, \ >>> + { "hotplug", 0, 0, OPT_HOTPLUG }, \ >>> #define KEXEC_OPT_STR "h?vdfixyluet:pscaS" >>> @@ -290,6 +293,8 @@ extern unsigned long add_buffer_phys_virt(struct kexec_info *info, >>> int buf_end, int phys); >>> extern void arch_reuse_initrd(void); >>> +extern long int get_nr_cpus(void); >>> + >>> extern int ifdown(void); >>> extern char purgatory[]; >>> >>> Regards, >>> eric >>> --- >>> >>> v9: 13jun2022 >>> - Rebased to 5.18.0 >>> - Per Sourabh, moved crash_prepare_elf64_headers() into common >>> crash_core.c to avoid compile issues with kexec_load only path. >>> - Per David Hildebrand, replaced mutex_trylock() with mutex_lock(). >>> - Changed the __weak arch_crash_handle_hotplug_event() to utilize >>> WARN_ONCE() instead of WARN(). Fix some formatting issues. >>> - Per Sourabh, introduced sysfs attribute crash_hotplug for memory >>> and CPUs; for use by userspace (udev) to determine if the kernel >>> performs crash hot un/plug support. >>> - Per Sourabh, moved the code detecting the elfcorehdr segment from >>> arch/x86 into crash_core:handle_hotplug_event() so both kexec_load >>> and kexec_file_load can benefit. >>> - Updated userspace kexec-tools kexec utility to reflect change to >>> using CRASH_MAX_MEMORY_RANGES and get_nr_cpus(). >>> >>> v8: 5may2022 >>> https://lkml.org/lkml/2022/5/5/1133 >>> - Per Borislav Petkov, eliminated CONFIG_CRASH_HOTPLUG in favor >>> of CONFIG_HOTPLUG_CPU || CONFIG_MEMORY_HOTPLUG, ie a new define >>> is not needed. Also use of IS_ENABLED() rather than #ifdef's. >>> Renamed crash_hotplug_handler() to handle_hotplug_event(). >>> And other corrections. >>> - Per Baoquan, minimized the parameters to the arch_crash_ >>> handle_hotplug_event() to hp_action and cpu. >>> - Introduce KEXEC_CRASH_HP_INVALID_CPU definition, per Baoquan. >>> - Per Sourabh Jain, renamed and repurposed CRASH_HOTPLUG_ELFCOREHDR_SZ >>> to CONFIG_CRASH_MAX_MEMORY_RANGES, mirroring kexec-tools change >>> by David Hildebrand. Folded this patch into the x86 >>> kexec_file_load support patch. >>> >>> v7: 13apr2022 >>> https://lkml.org/lkml/2022/4/13/850 >>> - Resolved parameter usage to crash_hotplug_handler(), per Baoquan. >>> >>> v6: 1apr2022 >>> https://lkml.org/lkml/2022/4/1/1203 >>> - Reword commit messages and some comment cleanup per Baoquan. >>> - Changed elf_index to elfcorehdr_index for clarity. >>> - Minor code changes per Baoquan. >>> >>> v5: 3mar2022 >>> https://lkml.org/lkml/2022/3/3/674 >>> - Reworded description of CRASH_HOTPLUG_ELFCOREHDR_SZ, per >>> David Hildenbrand. >>> - Refactored slightly a few patches per Baoquan recommendation. >>> >>> v4: 9feb2022 >>> https://lkml.org/lkml/2022/2/9/1406 >>> - Refactored patches per Baoquan suggestsions. >>> - A few corrections, per Baoquan. >>> >>> v3: 10jan2022 >>> https://lkml.org/lkml/2022/1/10/1212 >>> - Rebasing per Baoquan He request. >>> - Changed memory notifier per David Hildenbrand. >>> - Providing example kexec userspace change in cover letter. >>> >>> RFC v2: 7dec2021 >>> https://lkml.org/lkml/2021/12/7/1088 >>> - Acting upon Baoquan He suggestion of removing elfcorehdr from >>> the purgatory list of segments, removed purgatory code from >>> patchset, and it is signficiantly simpler now. >>> >>> RFC v1: 18nov2021 >>> https://lkml.org/lkml/2021/11/18/845 >>> - working patchset demonstrating kernel handling of hotplug >>> updates to x86 elfcorehdr for kexec_file_load >>> >>> RFC: 14dec2020 >>> https://lkml.org/lkml/2020/12/14/532 >>> - proposed concept of allowing kernel to handle hotplug update >>> of elfcorehdr >>> --- >>> >>> >>> Eric DeVolder (7): >>> crash: move crash_prepare_elf64_headers >>> crash: prototype change for crash_prepare_elf64_headers >>> crash: add generic infrastructure for crash hotplug support >>> kexec: exclude elfcorehdr from the segment digest >>> kexec: exclude hot remove cpu from elfcorehdr notes >>> crash: memory and cpu hotplug sysfs attributes >>> x86/crash: Add x86 crash hotplug support >>> >>> .../admin-guide/mm/memory-hotplug.rst | 8 + >>> Documentation/core-api/cpu_hotplug.rst | 18 ++ >>> arch/arm64/kernel/machine_kexec_file.c | 6 +- >>> arch/powerpc/kexec/file_load_64.c | 2 +- >>> arch/x86/Kconfig | 11 + >>> arch/x86/kernel/crash.c | 119 ++++++++- >>> drivers/base/cpu.c | 13 + >>> drivers/base/memory.c | 13 + >>> include/linux/crash_core.h | 12 + >>> include/linux/kexec.h | 14 +- >>> kernel/crash_core.c | 241 ++++++++++++++++++ >>> kernel/kexec_file.c | 105 +------- >>> 12 files changed, 456 insertions(+), 106 deletions(-) >>> >> >