Re: [PATCH v9 0/7] crash: Kernel handling of CPU and memory hot un/plug

Eric DeVolder
2022-07-05T15:18:38Z

Nudge...
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 <x86/x86-linux.h>
>
> 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(-)
>