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Date:   Wed, 20 Jul 2022 14:08:19 -0500
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Subject: Re: [PATCH v9 0/7] crash: Kernel handling of CPU and memory hot
 un/plug
Content-Language: en-US
From:   Eric DeVolder <eric.devolder@oracle.com>
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, vgoyal@redhat.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com,
        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        sourabhjain@linux.ibm.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com
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Baoquan,
I believe I've addressed all feedback, just checking to see if you agree.
I have the next patch set ready in the event you think it a good idea to post it.
Thanks!
eric


On 7/7/22 08:05, Eric DeVolder wrote:
> 
> 
> On 7/5/22 20:16, Baoquan He wrote:
>> 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?
> 
> 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 <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(-)
>>>>
>>>
>>