[PATCH v9 0/7] crash: Kernel handling of CPU and memory hot un/plug
Baoquan He
bhe at redhat.com
Tue Jul 5 18:16:01 PDT 2022
On 07/05/22 at 10:17am, Eric DeVolder wrote:
> Nudge...
> Thanks!
Seems DavidH has concern and rasied it after you posted v9. Is that
solved?
>
> 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(-)
> >
>
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