[PATCH v11 0/7] crash: Kernel handling of CPU and memory hot un/plug

[PATCH v11 0/7] crash: Kernel handling of CPU and memory hot un/plug

[Eric DeVolder]

When the kdump service is loaded, if a CPU or memory is hot
un/plugged, the crash elfcorehdr, 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
---
v11: 26aug2022
 - Rebased onto 6.0-rc2
 - Redid the rework of __weak to use asm/kexec.h, per Baoquan
 - Reworked some comments and minor items, per Baoquan

v10: 21jul2022
 https://lkml.org/lkml/2022/7/21/1007
 - Rebased to 5.19.0-rc7
 - Per Sourabh, corrected build issue with arch_un/map_crash_pages()
   for architectures not supporting this feature.
 - Per David Hildebrand, removed the WARN_ONCE() altogether.
 - Per David Hansen, converted to use of kmap_local_page().
 - Per Baoquan He, replaced use of __weak with the kexec technique.

v9: 13jun2022
 https://lkml.org/lkml/2022/6/13/3382
 - 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().
 - Updated the new proposed udev rules to reflect using the sysfs
   attributes crash_hotplug.

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/riscv/kernel/elf_kexec.c                 |   7 +-
 arch/x86/Kconfig                              |  11 +
 arch/x86/include/asm/kexec.h                  |  20 ++
 arch/x86/kernel/crash.c                       | 104 +++++++-
 drivers/base/cpu.c                            |  14 +
 drivers/base/memory.c                         |  13 +
 include/linux/crash_core.h                    |   8 +
 include/linux/kexec.h                         |  41 ++-
 kernel/crash_core.c                           | 249 ++++++++++++++++++
 kernel/kexec_file.c                           | 105 +-------
 14 files changed, 497 insertions(+), 109 deletions(-)

-- 
2.31.1


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[PATCH v11 0/7] crash: Kernel handling of CPU and memory hot un/plug

[Eric DeVolder]

When the kdump service is loaded, if a CPU or memory is hot
un/plugged, the crash elfcorehdr, 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
---
v11: 26aug2022
 - Rebased onto 6.0-rc2
 - Redid the rework of __weak to use asm/kexec.h, per Baoquan
 - Reworked some comments and minor items, per Baoquan

v10: 21jul2022
 https://lkml.org/lkml/2022/7/21/1007
 - Rebased to 5.19.0-rc7
 - Per Sourabh, corrected build issue with arch_un/map_crash_pages()
   for architectures not supporting this feature.
 - Per David Hildebrand, removed the WARN_ONCE() altogether.
 - Per David Hansen, converted to use of kmap_local_page().
 - Per Baoquan He, replaced use of __weak with the kexec technique.

v9: 13jun2022
 https://lkml.org/lkml/2022/6/13/3382
 - 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().
 - Updated the new proposed udev rules to reflect using the sysfs
   attributes crash_hotplug.

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/riscv/kernel/elf_kexec.c                 |   7 +-
 arch/x86/Kconfig                              |  11 +
 arch/x86/include/asm/kexec.h                  |  20 ++
 arch/x86/kernel/crash.c                       | 104 +++++++-
 drivers/base/cpu.c                            |  14 +
 drivers/base/memory.c                         |  13 +
 include/linux/crash_core.h                    |   8 +
 include/linux/kexec.h                         |  41 ++-
 kernel/crash_core.c                           | 249 ++++++++++++++++++
 kernel/kexec_file.c                           | 105 +-------
 14 files changed, 497 insertions(+), 109 deletions(-)

-- 
2.31.1

[PATCH v11 1/7] crash: move crash_prepare_elf64_headers

[Eric DeVolder]

At the outcome of this patch set, the crash_prepare_elf64_headers()
is utilized on both the kexec_file_load and kexec_load paths. As
such, need to move this function out of kexec_file.c and into a
common location crash_core.c.

No functionality change.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
 kernel/crash_core.c | 100 ++++++++++++++++++++++++++++++++++++++++++++
 kernel/kexec_file.c |  99 -------------------------------------------
 2 files changed, 100 insertions(+), 99 deletions(-)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 07b26df453a9..8c8c82386e8d 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -10,6 +10,7 @@
 #include <linux/utsname.h>
 #include <linux/vmalloc.h>
 #include <linux/sizes.h>
+#include <linux/kexec.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -314,6 +315,105 @@ static int __init parse_crashkernel_dummy(char *arg)
 }
 early_param("crashkernel", parse_crashkernel_dummy);
 
+int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
+			  void **addr, unsigned long *sz)
+{
+	Elf64_Ehdr *ehdr;
+	Elf64_Phdr *phdr;
+	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
+	unsigned char *buf;
+	unsigned int cpu, i;
+	unsigned long long notes_addr;
+	unsigned long mstart, mend;
+
+	/* extra phdr for vmcoreinfo ELF note */
+	nr_phdr = nr_cpus + 1;
+	nr_phdr += mem->nr_ranges;
+
+	/*
+	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
+	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
+	 * I think this is required by tools like gdb. So same physical
+	 * memory will be mapped in two ELF headers. One will contain kernel
+	 * text virtual addresses and other will have __va(physical) addresses.
+	 */
+
+	nr_phdr++;
+	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
+	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
+
+	buf = vzalloc(elf_sz);
+	if (!buf)
+		return -ENOMEM;
+
+	ehdr = (Elf64_Ehdr *)buf;
+	phdr = (Elf64_Phdr *)(ehdr + 1);
+	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
+	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
+	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
+	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
+	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
+	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
+	ehdr->e_type = ET_CORE;
+	ehdr->e_machine = ELF_ARCH;
+	ehdr->e_version = EV_CURRENT;
+	ehdr->e_phoff = sizeof(Elf64_Ehdr);
+	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
+	ehdr->e_phentsize = sizeof(Elf64_Phdr);
+
+	/* Prepare one phdr of type PT_NOTE for each present CPU */
+	for_each_present_cpu(cpu) {
+		phdr->p_type = PT_NOTE;
+		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
+		phdr->p_offset = phdr->p_paddr = notes_addr;
+		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
+		(ehdr->e_phnum)++;
+		phdr++;
+	}
+
+	/* Prepare one PT_NOTE header for vmcoreinfo */
+	phdr->p_type = PT_NOTE;
+	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
+	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
+	(ehdr->e_phnum)++;
+	phdr++;
+
+	/* Prepare PT_LOAD type program header for kernel text region */
+	if (need_kernel_map) {
+		phdr->p_type = PT_LOAD;
+		phdr->p_flags = PF_R|PF_W|PF_X;
+		phdr->p_vaddr = (unsigned long) _text;
+		phdr->p_filesz = phdr->p_memsz = _end - _text;
+		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
+		ehdr->e_phnum++;
+		phdr++;
+	}
+
+	/* Go through all the ranges in mem->ranges[] and prepare phdr */
+	for (i = 0; i < mem->nr_ranges; i++) {
+		mstart = mem->ranges[i].start;
+		mend = mem->ranges[i].end;
+
+		phdr->p_type = PT_LOAD;
+		phdr->p_flags = PF_R|PF_W|PF_X;
+		phdr->p_offset  = mstart;
+
+		phdr->p_paddr = mstart;
+		phdr->p_vaddr = (unsigned long) __va(mstart);
+		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
+		phdr->p_align = 0;
+		ehdr->e_phnum++;
+		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
+			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
+			ehdr->e_phnum, phdr->p_offset);
+		phdr++;
+	}
+
+	*addr = buf;
+	*sz = elf_sz;
+	return 0;
+}
+
 Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
 			  void *data, size_t data_len)
 {
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 1d546dc97c50..8017eeb43036 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -1217,102 +1217,3 @@ int crash_exclude_mem_range(struct crash_mem *mem,
 	mem->nr_ranges++;
 	return 0;
 }
-
-int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
-			  void **addr, unsigned long *sz)
-{
-	Elf64_Ehdr *ehdr;
-	Elf64_Phdr *phdr;
-	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
-	unsigned char *buf;
-	unsigned int cpu, i;
-	unsigned long long notes_addr;
-	unsigned long mstart, mend;
-
-	/* extra phdr for vmcoreinfo ELF note */
-	nr_phdr = nr_cpus + 1;
-	nr_phdr += mem->nr_ranges;
-
-	/*
-	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
-	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
-	 * I think this is required by tools like gdb. So same physical
-	 * memory will be mapped in two ELF headers. One will contain kernel
-	 * text virtual addresses and other will have __va(physical) addresses.
-	 */
-
-	nr_phdr++;
-	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
-	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
-
-	buf = vzalloc(elf_sz);
-	if (!buf)
-		return -ENOMEM;
-
-	ehdr = (Elf64_Ehdr *)buf;
-	phdr = (Elf64_Phdr *)(ehdr + 1);
-	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
-	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
-	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
-	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
-	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
-	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
-	ehdr->e_type = ET_CORE;
-	ehdr->e_machine = ELF_ARCH;
-	ehdr->e_version = EV_CURRENT;
-	ehdr->e_phoff = sizeof(Elf64_Ehdr);
-	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
-	ehdr->e_phentsize = sizeof(Elf64_Phdr);
-
-	/* Prepare one phdr of type PT_NOTE for each present CPU */
-	for_each_present_cpu(cpu) {
-		phdr->p_type = PT_NOTE;
-		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
-		phdr->p_offset = phdr->p_paddr = notes_addr;
-		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
-		(ehdr->e_phnum)++;
-		phdr++;
-	}
-
-	/* Prepare one PT_NOTE header for vmcoreinfo */
-	phdr->p_type = PT_NOTE;
-	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
-	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
-	(ehdr->e_phnum)++;
-	phdr++;
-
-	/* Prepare PT_LOAD type program header for kernel text region */
-	if (need_kernel_map) {
-		phdr->p_type = PT_LOAD;
-		phdr->p_flags = PF_R|PF_W|PF_X;
-		phdr->p_vaddr = (unsigned long) _text;
-		phdr->p_filesz = phdr->p_memsz = _end - _text;
-		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
-		ehdr->e_phnum++;
-		phdr++;
-	}
-
-	/* Go through all the ranges in mem->ranges[] and prepare phdr */
-	for (i = 0; i < mem->nr_ranges; i++) {
-		mstart = mem->ranges[i].start;
-		mend = mem->ranges[i].end;
-
-		phdr->p_type = PT_LOAD;
-		phdr->p_flags = PF_R|PF_W|PF_X;
-		phdr->p_offset  = mstart;
-
-		phdr->p_paddr = mstart;
-		phdr->p_vaddr = (unsigned long) __va(mstart);
-		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
-		phdr->p_align = 0;
-		ehdr->e_phnum++;
-		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
-			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
-			ehdr->e_phnum, phdr->p_offset);
-		phdr++;
-	}
-
-	*addr = buf;
-	*sz = elf_sz;
-	return 0;
-}
-- 
2.31.1

[PATCH v11 1/7] crash: move crash_prepare_elf64_headers

[Eric DeVolder]

At the outcome of this patch set, the crash_prepare_elf64_headers()
is utilized on both the kexec_file_load and kexec_load paths. As
such, need to move this function out of kexec_file.c and into a
common location crash_core.c.

No functionality change.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
 kernel/crash_core.c | 100 ++++++++++++++++++++++++++++++++++++++++++++
 kernel/kexec_file.c |  99 -------------------------------------------
 2 files changed, 100 insertions(+), 99 deletions(-)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 07b26df453a9..8c8c82386e8d 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -10,6 +10,7 @@
 #include <linux/utsname.h>
 #include <linux/vmalloc.h>
 #include <linux/sizes.h>
+#include <linux/kexec.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -314,6 +315,105 @@ static int __init parse_crashkernel_dummy(char *arg)
 }
 early_param("crashkernel", parse_crashkernel_dummy);
 
+int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
+			  void **addr, unsigned long *sz)
+{
+	Elf64_Ehdr *ehdr;
+	Elf64_Phdr *phdr;
+	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
+	unsigned char *buf;
+	unsigned int cpu, i;
+	unsigned long long notes_addr;
+	unsigned long mstart, mend;
+
+	/* extra phdr for vmcoreinfo ELF note */
+	nr_phdr = nr_cpus + 1;
+	nr_phdr += mem->nr_ranges;
+
+	/*
+	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
+	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
+	 * I think this is required by tools like gdb. So same physical
+	 * memory will be mapped in two ELF headers. One will contain kernel
+	 * text virtual addresses and other will have __va(physical) addresses.
+	 */
+
+	nr_phdr++;
+	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
+	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
+
+	buf = vzalloc(elf_sz);
+	if (!buf)
+		return -ENOMEM;
+
+	ehdr = (Elf64_Ehdr *)buf;
+	phdr = (Elf64_Phdr *)(ehdr + 1);
+	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
+	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
+	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
+	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
+	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
+	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
+	ehdr->e_type = ET_CORE;
+	ehdr->e_machine = ELF_ARCH;
+	ehdr->e_version = EV_CURRENT;
+	ehdr->e_phoff = sizeof(Elf64_Ehdr);
+	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
+	ehdr->e_phentsize = sizeof(Elf64_Phdr);
+
+	/* Prepare one phdr of type PT_NOTE for each present CPU */
+	for_each_present_cpu(cpu) {
+		phdr->p_type = PT_NOTE;
+		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
+		phdr->p_offset = phdr->p_paddr = notes_addr;
+		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
+		(ehdr->e_phnum)++;
+		phdr++;
+	}
+
+	/* Prepare one PT_NOTE header for vmcoreinfo */
+	phdr->p_type = PT_NOTE;
+	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
+	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
+	(ehdr->e_phnum)++;
+	phdr++;
+
+	/* Prepare PT_LOAD type program header for kernel text region */
+	if (need_kernel_map) {
+		phdr->p_type = PT_LOAD;
+		phdr->p_flags = PF_R|PF_W|PF_X;
+		phdr->p_vaddr = (unsigned long) _text;
+		phdr->p_filesz = phdr->p_memsz = _end - _text;
+		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
+		ehdr->e_phnum++;
+		phdr++;
+	}
+
+	/* Go through all the ranges in mem->ranges[] and prepare phdr */
+	for (i = 0; i < mem->nr_ranges; i++) {
+		mstart = mem->ranges[i].start;
+		mend = mem->ranges[i].end;
+
+		phdr->p_type = PT_LOAD;
+		phdr->p_flags = PF_R|PF_W|PF_X;
+		phdr->p_offset  = mstart;
+
+		phdr->p_paddr = mstart;
+		phdr->p_vaddr = (unsigned long) __va(mstart);
+		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
+		phdr->p_align = 0;
+		ehdr->e_phnum++;
+		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
+			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
+			ehdr->e_phnum, phdr->p_offset);
+		phdr++;
+	}
+
+	*addr = buf;
+	*sz = elf_sz;
+	return 0;
+}
+
 Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
 			  void *data, size_t data_len)
 {
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 1d546dc97c50..8017eeb43036 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -1217,102 +1217,3 @@ int crash_exclude_mem_range(struct crash_mem *mem,
 	mem->nr_ranges++;
 	return 0;
 }
-
-int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
-			  void **addr, unsigned long *sz)
-{
-	Elf64_Ehdr *ehdr;
-	Elf64_Phdr *phdr;
-	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
-	unsigned char *buf;
-	unsigned int cpu, i;
-	unsigned long long notes_addr;
-	unsigned long mstart, mend;
-
-	/* extra phdr for vmcoreinfo ELF note */
-	nr_phdr = nr_cpus + 1;
-	nr_phdr += mem->nr_ranges;
-
-	/*
-	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
-	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
-	 * I think this is required by tools like gdb. So same physical
-	 * memory will be mapped in two ELF headers. One will contain kernel
-	 * text virtual addresses and other will have __va(physical) addresses.
-	 */
-
-	nr_phdr++;
-	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
-	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
-
-	buf = vzalloc(elf_sz);
-	if (!buf)
-		return -ENOMEM;
-
-	ehdr = (Elf64_Ehdr *)buf;
-	phdr = (Elf64_Phdr *)(ehdr + 1);
-	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
-	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
-	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
-	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
-	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
-	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
-	ehdr->e_type = ET_CORE;
-	ehdr->e_machine = ELF_ARCH;
-	ehdr->e_version = EV_CURRENT;
-	ehdr->e_phoff = sizeof(Elf64_Ehdr);
-	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
-	ehdr->e_phentsize = sizeof(Elf64_Phdr);
-
-	/* Prepare one phdr of type PT_NOTE for each present CPU */
-	for_each_present_cpu(cpu) {
-		phdr->p_type = PT_NOTE;
-		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
-		phdr->p_offset = phdr->p_paddr = notes_addr;
-		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
-		(ehdr->e_phnum)++;
-		phdr++;
-	}
-
-	/* Prepare one PT_NOTE header for vmcoreinfo */
-	phdr->p_type = PT_NOTE;
-	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
-	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
-	(ehdr->e_phnum)++;
-	phdr++;
-
-	/* Prepare PT_LOAD type program header for kernel text region */
-	if (need_kernel_map) {
-		phdr->p_type = PT_LOAD;
-		phdr->p_flags = PF_R|PF_W|PF_X;
-		phdr->p_vaddr = (unsigned long) _text;
-		phdr->p_filesz = phdr->p_memsz = _end - _text;
-		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
-		ehdr->e_phnum++;
-		phdr++;
-	}
-
-	/* Go through all the ranges in mem->ranges[] and prepare phdr */
-	for (i = 0; i < mem->nr_ranges; i++) {
-		mstart = mem->ranges[i].start;
-		mend = mem->ranges[i].end;
-
-		phdr->p_type = PT_LOAD;
-		phdr->p_flags = PF_R|PF_W|PF_X;
-		phdr->p_offset  = mstart;
-
-		phdr->p_paddr = mstart;
-		phdr->p_vaddr = (unsigned long) __va(mstart);
-		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
-		phdr->p_align = 0;
-		ehdr->e_phnum++;
-		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
-			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
-			ehdr->e_phnum, phdr->p_offset);
-		phdr++;
-	}
-
-	*addr = buf;
-	*sz = elf_sz;
-	return 0;
-}
-- 
2.31.1


_______________________________________________
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kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCH v11 2/7] crash: prototype change for crash_prepare_elf64_headers

[Eric DeVolder]

From within crash_prepare_elf64_headers() there is a need to
reference the struct kimage hotplug members. As such, this
change passes the struct kimage as a parameter to the
crash_prepare_elf64_headers(). The hotplug members are added
in "crash: add generic infrastructure for crash hotplug support".

This is preparation for later patch, no functionality change.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
---
 arch/arm64/kernel/machine_kexec_file.c | 6 +++---
 arch/powerpc/kexec/file_load_64.c      | 2 +-
 arch/riscv/kernel/elf_kexec.c          | 7 ++++---
 arch/x86/kernel/crash.c                | 2 +-
 include/linux/kexec.h                  | 7 +++++--
 kernel/crash_core.c                    | 4 ++--
 6 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index 889951291cc0..7f5f8243928e 100644
--- a/arch/arm64/kernel/machine_kexec_file.c
+++ b/arch/arm64/kernel/machine_kexec_file.c
@@ -39,7 +39,7 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
 	return kexec_image_post_load_cleanup_default(image);
 }
 
-static int prepare_elf_headers(void **addr, unsigned long *sz)
+static int prepare_elf_headers(struct kimage *image, void **addr, unsigned long *sz)
 {
 	struct crash_mem *cmem;
 	unsigned int nr_ranges;
@@ -64,7 +64,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 	}
 
 	/* Exclude crashkernel region */
-	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
+	ret = crash_exclude_mem_range(image, cmem, crashk_res.start, crashk_res.end);
 	if (ret)
 		goto out;
 
@@ -74,7 +74,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 			goto out;
 	}
 
-	ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
+	ret = crash_prepare_elf64_headers(image, cmem, true, addr, sz);
 
 out:
 	kfree(cmem);
diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
index 349a781cea0b..a0af9966a8f0 100644
--- a/arch/powerpc/kexec/file_load_64.c
+++ b/arch/powerpc/kexec/file_load_64.c
@@ -798,7 +798,7 @@ static int load_elfcorehdr_segment(struct kimage *image, struct kexec_buf *kbuf)
 		goto out;
 
 	/* Setup elfcorehdr segment */
-	ret = crash_prepare_elf64_headers(cmem, false, &headers, &headers_sz);
+	ret = crash_prepare_elf64_headers(image, cmem, false, &headers, &headers_sz);
 	if (ret) {
 		pr_err("Failed to prepare elf headers for the core\n");
 		goto out;
diff --git a/arch/riscv/kernel/elf_kexec.c b/arch/riscv/kernel/elf_kexec.c
index 0cb94992c15b..ffde73228108 100644
--- a/arch/riscv/kernel/elf_kexec.c
+++ b/arch/riscv/kernel/elf_kexec.c
@@ -118,7 +118,8 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
 	return 0;
 }
 
-static int prepare_elf_headers(void **addr, unsigned long *sz)
+static int prepare_elf_headers(struct kimage *image,
+	void **addr, unsigned long *sz)
 {
 	struct crash_mem *cmem;
 	unsigned int nr_ranges;
@@ -140,7 +141,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 	/* Exclude crashkernel region */
 	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
 	if (!ret)
-		ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
+		ret = crash_prepare_elf64_headers(image, cmem, true, addr, sz);
 
 out:
 	kfree(cmem);
@@ -212,7 +213,7 @@ static void *elf_kexec_load(struct kimage *image, char *kernel_buf,
 
 	/* Add elfcorehdr */
 	if (image->type == KEXEC_TYPE_CRASH) {
-		ret = prepare_elf_headers(&headers, &headers_sz);
+		ret = prepare_elf_headers(image, &headers, &headers_sz);
 		if (ret) {
 			pr_err("Preparing elf core header failed\n");
 			goto out;
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9730c88530fc..9ceb93c176a6 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -265,7 +265,7 @@ static int prepare_elf_headers(struct kimage *image, void **addr,
 		goto out;
 
 	/* By default prepare 64bit headers */
-	ret =  crash_prepare_elf64_headers(cmem, IS_ENABLED(CONFIG_X86_64), addr, sz);
+	ret =  crash_prepare_elf64_headers(image, cmem, IS_ENABLED(CONFIG_X86_64), addr, sz);
 
 out:
 	vfree(cmem);
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 13e6c4b58f07..4eefa631e0ae 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -253,8 +253,11 @@ struct crash_mem {
 extern int crash_exclude_mem_range(struct crash_mem *mem,
 				   unsigned long long mstart,
 				   unsigned long long mend);
-extern int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
-				       void **addr, unsigned long *sz);
+extern int crash_prepare_elf64_headers(struct kimage *image,
+				   struct crash_mem *mem,
+				   int need_kernel_map,
+				   void **addr,
+				   unsigned long *sz);
 
 #ifndef arch_kexec_apply_relocations_add
 /*
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 8c8c82386e8d..0f8aa659cca4 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -315,8 +315,8 @@ static int __init parse_crashkernel_dummy(char *arg)
 }
 early_param("crashkernel", parse_crashkernel_dummy);
 
-int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
-			  void **addr, unsigned long *sz)
+int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
+			  int need_kernel_map, void **addr, unsigned long *sz)
 {
 	Elf64_Ehdr *ehdr;
 	Elf64_Phdr *phdr;
-- 
2.31.1

[PATCH v11 2/7] crash: prototype change for crash_prepare_elf64_headers

[Eric DeVolder]

From within crash_prepare_elf64_headers() there is a need to
reference the struct kimage hotplug members. As such, this
change passes the struct kimage as a parameter to the
crash_prepare_elf64_headers(). The hotplug members are added
in "crash: add generic infrastructure for crash hotplug support".

This is preparation for later patch, no functionality change.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
---
 arch/arm64/kernel/machine_kexec_file.c | 6 +++---
 arch/powerpc/kexec/file_load_64.c      | 2 +-
 arch/riscv/kernel/elf_kexec.c          | 7 ++++---
 arch/x86/kernel/crash.c                | 2 +-
 include/linux/kexec.h                  | 7 +++++--
 kernel/crash_core.c                    | 4 ++--
 6 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index 889951291cc0..7f5f8243928e 100644
--- a/arch/arm64/kernel/machine_kexec_file.c
+++ b/arch/arm64/kernel/machine_kexec_file.c
@@ -39,7 +39,7 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
 	return kexec_image_post_load_cleanup_default(image);
 }
 
-static int prepare_elf_headers(void **addr, unsigned long *sz)
+static int prepare_elf_headers(struct kimage *image, void **addr, unsigned long *sz)
 {
 	struct crash_mem *cmem;
 	unsigned int nr_ranges;
@@ -64,7 +64,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 	}
 
 	/* Exclude crashkernel region */
-	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
+	ret = crash_exclude_mem_range(image, cmem, crashk_res.start, crashk_res.end);
 	if (ret)
 		goto out;
 
@@ -74,7 +74,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 			goto out;
 	}
 
-	ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
+	ret = crash_prepare_elf64_headers(image, cmem, true, addr, sz);
 
 out:
 	kfree(cmem);
diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
index 349a781cea0b..a0af9966a8f0 100644
--- a/arch/powerpc/kexec/file_load_64.c
+++ b/arch/powerpc/kexec/file_load_64.c
@@ -798,7 +798,7 @@ static int load_elfcorehdr_segment(struct kimage *image, struct kexec_buf *kbuf)
 		goto out;
 
 	/* Setup elfcorehdr segment */
-	ret = crash_prepare_elf64_headers(cmem, false, &headers, &headers_sz);
+	ret = crash_prepare_elf64_headers(image, cmem, false, &headers, &headers_sz);
 	if (ret) {
 		pr_err("Failed to prepare elf headers for the core\n");
 		goto out;
diff --git a/arch/riscv/kernel/elf_kexec.c b/arch/riscv/kernel/elf_kexec.c
index 0cb94992c15b..ffde73228108 100644
--- a/arch/riscv/kernel/elf_kexec.c
+++ b/arch/riscv/kernel/elf_kexec.c
@@ -118,7 +118,8 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
 	return 0;
 }
 
-static int prepare_elf_headers(void **addr, unsigned long *sz)
+static int prepare_elf_headers(struct kimage *image,
+	void **addr, unsigned long *sz)
 {
 	struct crash_mem *cmem;
 	unsigned int nr_ranges;
@@ -140,7 +141,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 	/* Exclude crashkernel region */
 	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
 	if (!ret)
-		ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
+		ret = crash_prepare_elf64_headers(image, cmem, true, addr, sz);
 
 out:
 	kfree(cmem);
@@ -212,7 +213,7 @@ static void *elf_kexec_load(struct kimage *image, char *kernel_buf,
 
 	/* Add elfcorehdr */
 	if (image->type == KEXEC_TYPE_CRASH) {
-		ret = prepare_elf_headers(&headers, &headers_sz);
+		ret = prepare_elf_headers(image, &headers, &headers_sz);
 		if (ret) {
 			pr_err("Preparing elf core header failed\n");
 			goto out;
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9730c88530fc..9ceb93c176a6 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -265,7 +265,7 @@ static int prepare_elf_headers(struct kimage *image, void **addr,
 		goto out;
 
 	/* By default prepare 64bit headers */
-	ret =  crash_prepare_elf64_headers(cmem, IS_ENABLED(CONFIG_X86_64), addr, sz);
+	ret =  crash_prepare_elf64_headers(image, cmem, IS_ENABLED(CONFIG_X86_64), addr, sz);
 
 out:
 	vfree(cmem);
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 13e6c4b58f07..4eefa631e0ae 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -253,8 +253,11 @@ struct crash_mem {
 extern int crash_exclude_mem_range(struct crash_mem *mem,
 				   unsigned long long mstart,
 				   unsigned long long mend);
-extern int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
-				       void **addr, unsigned long *sz);
+extern int crash_prepare_elf64_headers(struct kimage *image,
+				   struct crash_mem *mem,
+				   int need_kernel_map,
+				   void **addr,
+				   unsigned long *sz);
 
 #ifndef arch_kexec_apply_relocations_add
 /*
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 8c8c82386e8d..0f8aa659cca4 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -315,8 +315,8 @@ static int __init parse_crashkernel_dummy(char *arg)
 }
 early_param("crashkernel", parse_crashkernel_dummy);
 
-int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
-			  void **addr, unsigned long *sz)
+int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
+			  int need_kernel_map, void **addr, unsigned long *sz)
 {
 	Elf64_Ehdr *ehdr;
 	Elf64_Phdr *phdr;
-- 
2.31.1


_______________________________________________
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kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support

[Eric DeVolder]

CPU and memory change notifications are received in order to
regenerate the elfcorehdr.

To support cpu hotplug, a callback is registered to capture the
CPUHP_AP_ONLINE_DYN online and offline events via
cpuhp_setup_state_nocalls().

To support memory hotplug, a notifier is registered to capture the
MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().

The cpu callback and memory notifiers call handle_hotplug_event()
which performs needed tasks and then dispatches the event to the
architecture specific arch_crash_handle_hotplug_event(). During the
process, the kexec_mutex is held.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
 include/linux/crash_core.h |   8 +++
 include/linux/kexec.h      |  26 +++++++
 kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
 3 files changed, 168 insertions(+)

diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index de62a722431e..3b99e69b011f 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
 int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
 		unsigned long long *crash_size, unsigned long long *crash_base);
 
+#define KEXEC_CRASH_HP_REMOVE_CPU		0
+#define KEXEC_CRASH_HP_ADD_CPU			1
+#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
+#define KEXEC_CRASH_HP_ADD_MEMORY		3
+#define KEXEC_CRASH_HP_INVALID_CPU		-1U
+
+struct kimage;
+
 #endif /* LINUX_CRASH_CORE_H */
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 4eefa631e0ae..9597b41136ec 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -374,6 +374,13 @@ struct kimage {
 	struct purgatory_info purgatory_info;
 #endif
 
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+	bool hotplug_event;
+	unsigned int offlinecpu;
+	bool elfcorehdr_index_valid;
+	int elfcorehdr_index;
+#endif
+
 #ifdef CONFIG_IMA_KEXEC
 	/* Virtual address of IMA measurement buffer for kexec syscall */
 	void *ima_buffer;
@@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
 static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
 #endif
 
+#ifndef arch_map_crash_pages
+static inline void *arch_map_crash_pages(unsigned long paddr,
+		unsigned long size)
+{
+	return NULL;
+}
+#endif
+
+#ifndef arch_unmap_crash_pages
+static inline void arch_unmap_crash_pages(void **ptr) { }
+#endif
+
+#ifndef arch_crash_handle_hotplug_event
+static inline void arch_crash_handle_hotplug_event(struct kimage *image,
+		unsigned int hp_action)
+{
+}
+#endif
+
 #else /* !CONFIG_KEXEC_CORE */
 struct pt_regs;
 struct task_struct;
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 0f8aa659cca4..455150205ded 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -11,6 +11,8 @@
 #include <linux/vmalloc.h>
 #include <linux/sizes.h>
 #include <linux/kexec.h>
+#include <linux/memory.h>
+#include <linux/cpuhotplug.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -18,6 +20,7 @@
 #include <crypto/sha1.h>
 
 #include "kallsyms_internal.h"
+#include "kexec_internal.h"
 
 /* vmcoreinfo stuff */
 unsigned char *vmcoreinfo_data;
@@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
 }
 
 subsys_initcall(crash_save_vmcoreinfo_init);
+
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+/*
+ * 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.
+ *
+ * In order to make changes to elfcorehdr, two conditions are needed:
+ * First, the segment containing the elfcorehdr must be large enough
+ * to permit a growing number of resources. The elfcorehdr memory is
+ * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
+ * 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).
+ */
+static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
+{
+	/* Obtain lock while changing crash information */
+	mutex_lock(&kexec_mutex);
+
+	/* Check kdump is loaded */
+	if (kexec_crash_image) {
+		struct kimage *image = kexec_crash_image;
+
+		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
+			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
+			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
+		else
+			pr_debug("crash hp: hp_action %u", hp_action);
+
+		/*
+		 * When the struct kimage is alloced, it is wiped to zero, so
+		 * the elfcorehdr_index_valid defaults to false. Find the
+		 * segment containing the elfcorehdr, if not already found.
+		 * This works for both the kexec_load and kexec_file_load paths.
+		 */
+		if (!image->elfcorehdr_index_valid) {
+			unsigned char *ptr;
+			unsigned long mem, memsz;
+			unsigned int n;
+
+			for (n = 0; n < image->nr_segments; n++) {
+				mem = image->segment[n].mem;
+				memsz = image->segment[n].memsz;
+				ptr = arch_map_crash_pages(mem, memsz);
+				if (ptr) {
+					/* The segment containing elfcorehdr */
+					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
+						image->elfcorehdr_index = (int)n;
+						image->elfcorehdr_index_valid = true;
+					}
+				}
+				arch_unmap_crash_pages((void **)&ptr);
+			}
+		}
+
+		if (!image->elfcorehdr_index_valid) {
+			pr_err("crash hp: unable to locate elfcorehdr segment");
+			goto out;
+		}
+
+		/* Needed in order for the segments to be updated */
+		arch_kexec_unprotect_crashkres();
+
+		/* Flag to differentiate between normal load and hotplug */
+		image->hotplug_event = true;
+
+		/* Now invoke arch-specific update handler */
+		arch_crash_handle_hotplug_event(image, hp_action);
+
+		/* No longer handling a hotplug event */
+		image->hotplug_event = false;
+
+		/* Change back to read-only */
+		arch_kexec_protect_crashkres();
+	}
+
+out:
+	/* Release lock now that update complete */
+	mutex_unlock(&kexec_mutex);
+}
+
+static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
+{
+	switch (val) {
+	case MEM_ONLINE:
+		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
+		break;
+
+	case MEM_OFFLINE:
+		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block crash_memhp_nb = {
+	.notifier_call = crash_memhp_notifier,
+	.priority = 0
+};
+
+static int crash_cpuhp_online(unsigned int cpu)
+{
+	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
+	return 0;
+}
+
+static int crash_cpuhp_offline(unsigned int cpu)
+{
+	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
+	return 0;
+}
+
+static int __init crash_hotplug_init(void)
+{
+	int result = 0;
+
+	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+		register_memory_notifier(&crash_memhp_nb);
+
+	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
+		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+						   "crash/cpuhp",
+						   crash_cpuhp_online,
+						   crash_cpuhp_offline);
+
+	return result;
+}
+
+subsys_initcall(crash_hotplug_init);
+#endif
-- 
2.31.1


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[PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support

[Eric DeVolder]

CPU and memory change notifications are received in order to
regenerate the elfcorehdr.

To support cpu hotplug, a callback is registered to capture the
CPUHP_AP_ONLINE_DYN online and offline events via
cpuhp_setup_state_nocalls().

To support memory hotplug, a notifier is registered to capture the
MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().

The cpu callback and memory notifiers call handle_hotplug_event()
which performs needed tasks and then dispatches the event to the
architecture specific arch_crash_handle_hotplug_event(). During the
process, the kexec_mutex is held.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
 include/linux/crash_core.h |   8 +++
 include/linux/kexec.h      |  26 +++++++
 kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
 3 files changed, 168 insertions(+)

diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index de62a722431e..3b99e69b011f 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
 int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
 		unsigned long long *crash_size, unsigned long long *crash_base);
 
+#define KEXEC_CRASH_HP_REMOVE_CPU		0
+#define KEXEC_CRASH_HP_ADD_CPU			1
+#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
+#define KEXEC_CRASH_HP_ADD_MEMORY		3
+#define KEXEC_CRASH_HP_INVALID_CPU		-1U
+
+struct kimage;
+
 #endif /* LINUX_CRASH_CORE_H */
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 4eefa631e0ae..9597b41136ec 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -374,6 +374,13 @@ struct kimage {
 	struct purgatory_info purgatory_info;
 #endif
 
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+	bool hotplug_event;
+	unsigned int offlinecpu;
+	bool elfcorehdr_index_valid;
+	int elfcorehdr_index;
+#endif
+
 #ifdef CONFIG_IMA_KEXEC
 	/* Virtual address of IMA measurement buffer for kexec syscall */
 	void *ima_buffer;
@@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
 static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
 #endif
 
+#ifndef arch_map_crash_pages
+static inline void *arch_map_crash_pages(unsigned long paddr,
+		unsigned long size)
+{
+	return NULL;
+}
+#endif
+
+#ifndef arch_unmap_crash_pages
+static inline void arch_unmap_crash_pages(void **ptr) { }
+#endif
+
+#ifndef arch_crash_handle_hotplug_event
+static inline void arch_crash_handle_hotplug_event(struct kimage *image,
+		unsigned int hp_action)
+{
+}
+#endif
+
 #else /* !CONFIG_KEXEC_CORE */
 struct pt_regs;
 struct task_struct;
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 0f8aa659cca4..455150205ded 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -11,6 +11,8 @@
 #include <linux/vmalloc.h>
 #include <linux/sizes.h>
 #include <linux/kexec.h>
+#include <linux/memory.h>
+#include <linux/cpuhotplug.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -18,6 +20,7 @@
 #include <crypto/sha1.h>
 
 #include "kallsyms_internal.h"
+#include "kexec_internal.h"
 
 /* vmcoreinfo stuff */
 unsigned char *vmcoreinfo_data;
@@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
 }
 
 subsys_initcall(crash_save_vmcoreinfo_init);
+
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+/*
+ * 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.
+ *
+ * In order to make changes to elfcorehdr, two conditions are needed:
+ * First, the segment containing the elfcorehdr must be large enough
+ * to permit a growing number of resources. The elfcorehdr memory is
+ * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
+ * 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).
+ */
+static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
+{
+	/* Obtain lock while changing crash information */
+	mutex_lock(&kexec_mutex);
+
+	/* Check kdump is loaded */
+	if (kexec_crash_image) {
+		struct kimage *image = kexec_crash_image;
+
+		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
+			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
+			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
+		else
+			pr_debug("crash hp: hp_action %u", hp_action);
+
+		/*
+		 * When the struct kimage is alloced, it is wiped to zero, so
+		 * the elfcorehdr_index_valid defaults to false. Find the
+		 * segment containing the elfcorehdr, if not already found.
+		 * This works for both the kexec_load and kexec_file_load paths.
+		 */
+		if (!image->elfcorehdr_index_valid) {
+			unsigned char *ptr;
+			unsigned long mem, memsz;
+			unsigned int n;
+
+			for (n = 0; n < image->nr_segments; n++) {
+				mem = image->segment[n].mem;
+				memsz = image->segment[n].memsz;
+				ptr = arch_map_crash_pages(mem, memsz);
+				if (ptr) {
+					/* The segment containing elfcorehdr */
+					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
+						image->elfcorehdr_index = (int)n;
+						image->elfcorehdr_index_valid = true;
+					}
+				}
+				arch_unmap_crash_pages((void **)&ptr);
+			}
+		}
+
+		if (!image->elfcorehdr_index_valid) {
+			pr_err("crash hp: unable to locate elfcorehdr segment");
+			goto out;
+		}
+
+		/* Needed in order for the segments to be updated */
+		arch_kexec_unprotect_crashkres();
+
+		/* Flag to differentiate between normal load and hotplug */
+		image->hotplug_event = true;
+
+		/* Now invoke arch-specific update handler */
+		arch_crash_handle_hotplug_event(image, hp_action);
+
+		/* No longer handling a hotplug event */
+		image->hotplug_event = false;
+
+		/* Change back to read-only */
+		arch_kexec_protect_crashkres();
+	}
+
+out:
+	/* Release lock now that update complete */
+	mutex_unlock(&kexec_mutex);
+}
+
+static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
+{
+	switch (val) {
+	case MEM_ONLINE:
+		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
+		break;
+
+	case MEM_OFFLINE:
+		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block crash_memhp_nb = {
+	.notifier_call = crash_memhp_notifier,
+	.priority = 0
+};
+
+static int crash_cpuhp_online(unsigned int cpu)
+{
+	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
+	return 0;
+}
+
+static int crash_cpuhp_offline(unsigned int cpu)
+{
+	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
+	return 0;
+}
+
+static int __init crash_hotplug_init(void)
+{
+	int result = 0;
+
+	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+		register_memory_notifier(&crash_memhp_nb);
+
+	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
+		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+						   "crash/cpuhp",
+						   crash_cpuhp_online,
+						   crash_cpuhp_offline);
+
+	return result;
+}
+
+subsys_initcall(crash_hotplug_init);
+#endif
-- 
2.31.1

[PATCH v11 4/7] kexec: exclude elfcorehdr from the segment digest

[Eric DeVolder]

When a crash kernel is loaded via the kexec_file_load syscall, the
kernel places the various segments (ie crash kernel, crash initrd,
boot_params, elfcorehdr, purgatory, etc) in memory. For those
architectures that utilize purgatory, a hash digest of the segments
is calculated for integrity checking. This digest is embedded into
the purgatory image prior to placing purgatory in memory.

Since hotplug events cause changes to the elfcorehdr, purgatory
integrity checking fails (at crash time, and no kdump created).
As a result, this change explicitly excludes the elfcorehdr segment
from the list of segments used to create the digest. By doing so,
this permits changes to the elfcorehdr in response to hotplug events,
without having to also reload purgatory due to the change to the
digest.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 kernel/kexec_file.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 8017eeb43036..d0c2661b3509 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -723,6 +723,12 @@ static int kexec_calculate_store_digests(struct kimage *image)
 	for (j = i = 0; i < image->nr_segments; i++) {
 		struct kexec_segment *ksegment;
 
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+		/* Exclude elfcorehdr segment to allow future changes via hotplug */
+		if (image->elfcorehdr_index_valid && (j == image->elfcorehdr_index))
+			continue;
+#endif
+
 		ksegment = &image->segment[i];
 		/*
 		 * Skip purgatory as it will be modified once we put digest
-- 
2.31.1


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[PATCH v11 4/7] kexec: exclude elfcorehdr from the segment digest

[Eric DeVolder]

When a crash kernel is loaded via the kexec_file_load syscall, the
kernel places the various segments (ie crash kernel, crash initrd,
boot_params, elfcorehdr, purgatory, etc) in memory. For those
architectures that utilize purgatory, a hash digest of the segments
is calculated for integrity checking. This digest is embedded into
the purgatory image prior to placing purgatory in memory.

Since hotplug events cause changes to the elfcorehdr, purgatory
integrity checking fails (at crash time, and no kdump created).
As a result, this change explicitly excludes the elfcorehdr segment
from the list of segments used to create the digest. By doing so,
this permits changes to the elfcorehdr in response to hotplug events,
without having to also reload purgatory due to the change to the
digest.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 kernel/kexec_file.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 8017eeb43036..d0c2661b3509 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -723,6 +723,12 @@ static int kexec_calculate_store_digests(struct kimage *image)
 	for (j = i = 0; i < image->nr_segments; i++) {
 		struct kexec_segment *ksegment;
 
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+		/* Exclude elfcorehdr segment to allow future changes via hotplug */
+		if (image->elfcorehdr_index_valid && (j == image->elfcorehdr_index))
+			continue;
+#endif
+
 		ksegment = &image->segment[i];
 		/*
 		 * Skip purgatory as it will be modified once we put digest
-- 
2.31.1

[PATCH v11 5/7] kexec: exclude hot remove cpu from elfcorehdr notes

[Eric DeVolder]

Due to use of CPUHP_AP_ONLINE_DYN, upon CPU unplug, the CPU is
still in the for_each_present_cpu() list when within the
handle_hotplug_event(). Thus the CPU must be explicitly excluded
when building the new list of CPUs.

This change identifies in handle_hotplug_event() the CPU to be
excluded, and the check for excluding the CPU in
crash_prepare_elf64_headers().

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 kernel/crash_core.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 455150205ded..2f84a221b370 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -366,6 +366,11 @@ int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
 
 	/* Prepare one phdr of type PT_NOTE for each present CPU */
 	for_each_present_cpu(cpu) {
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+		/* Skip the soon-to-be offlined cpu */
+		if (image->hotplug_event && (cpu == image->offlinecpu))
+			continue;
+#endif
 		phdr->p_type = PT_NOTE;
 		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
 		phdr->p_offset = phdr->p_paddr = notes_addr;
@@ -681,6 +686,16 @@ static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
 		/* Flag to differentiate between normal load and hotplug */
 		image->hotplug_event = true;
 
+		/*
+		 * Due to use of CPUHP_AP_ONLINE_DYN, upon unplug and during
+		 * this callback, the CPU is still in the for_each_present_cpu()
+		 * list. Must explicitly look to exclude this CPU when building
+		 * new list.
+		 */
+		image->offlinecpu =
+			(hp_action == KEXEC_CRASH_HP_REMOVE_CPU) ?
+				cpu : KEXEC_CRASH_HP_INVALID_CPU;
+
 		/* Now invoke arch-specific update handler */
 		arch_crash_handle_hotplug_event(image, hp_action);
 
-- 
2.31.1

[PATCH v11 5/7] kexec: exclude hot remove cpu from elfcorehdr notes

[Eric DeVolder]

Due to use of CPUHP_AP_ONLINE_DYN, upon CPU unplug, the CPU is
still in the for_each_present_cpu() list when within the
handle_hotplug_event(). Thus the CPU must be explicitly excluded
when building the new list of CPUs.

This change identifies in handle_hotplug_event() the CPU to be
excluded, and the check for excluding the CPU in
crash_prepare_elf64_headers().

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 kernel/crash_core.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 455150205ded..2f84a221b370 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -366,6 +366,11 @@ int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
 
 	/* Prepare one phdr of type PT_NOTE for each present CPU */
 	for_each_present_cpu(cpu) {
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+		/* Skip the soon-to-be offlined cpu */
+		if (image->hotplug_event && (cpu == image->offlinecpu))
+			continue;
+#endif
 		phdr->p_type = PT_NOTE;
 		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
 		phdr->p_offset = phdr->p_paddr = notes_addr;
@@ -681,6 +686,16 @@ static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
 		/* Flag to differentiate between normal load and hotplug */
 		image->hotplug_event = true;
 
+		/*
+		 * Due to use of CPUHP_AP_ONLINE_DYN, upon unplug and during
+		 * this callback, the CPU is still in the for_each_present_cpu()
+		 * list. Must explicitly look to exclude this CPU when building
+		 * new list.
+		 */
+		image->offlinecpu =
+			(hp_action == KEXEC_CRASH_HP_REMOVE_CPU) ?
+				cpu : KEXEC_CRASH_HP_INVALID_CPU;
+
 		/* Now invoke arch-specific update handler */
 		arch_crash_handle_hotplug_event(image, hp_action);
 
-- 
2.31.1


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[PATCH v11 6/7] crash: memory and cpu hotplug sysfs attributes

[Eric DeVolder]

This introduces the crash_hotplug attribute for memory and CPUs
for use by userspace.  This change directly facilitates the udev
rule for managing userspace re-loading of the crash kernel upon
hot un/plug changes.

For memory, this changeset introduces the crash_hotplug attribute
to the /sys/devices/system/memory directory. For example:

 # udevadm info --attribute-walk /sys/devices/system/memory/memory81
  looking at device '/devices/system/memory/memory81':
    KERNEL=="memory81"
    SUBSYSTEM=="memory"
    DRIVER==""
    ATTR{online}=="1"
    ATTR{phys_device}=="0"
    ATTR{phys_index}=="00000051"
    ATTR{removable}=="1"
    ATTR{state}=="online"
    ATTR{valid_zones}=="Movable"

  looking at parent device '/devices/system/memory':
    KERNELS=="memory"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{auto_online_blocks}=="offline"
    ATTRS{block_size_bytes}=="8000000"
    ATTRS{crash_hotplug}=="1"

For CPUs, this changeset introduces the crash_hotplug attribute
to the /sys/devices/system/cpu directory. For example:

 # udevadm info --attribute-walk /sys/devices/system/cpu/cpu0
  looking at device '/devices/system/cpu/cpu0':
    KERNEL=="cpu0"
    SUBSYSTEM=="cpu"
    DRIVER=="processor"
    ATTR{crash_notes}=="277c38600"
    ATTR{crash_notes_size}=="368"
    ATTR{online}=="1"

  looking at parent device '/devices/system/cpu':
    KERNELS=="cpu"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{crash_hotplug}=="1"
    ATTRS{isolated}==""
    ATTRS{kernel_max}=="8191"
    ATTRS{nohz_full}=="  (null)"
    ATTRS{offline}=="4-7"
    ATTRS{online}=="0-3"
    ATTRS{possible}=="0-7"
    ATTRS{present}=="0-3"

With these sysfs attributes in place, it is possible to efficiently
instruct the udev rule to skip crash kernel reloading.

For example, the following is the proposed udev rule change for RHEL
system 98-kexec.rules (as the first lines of the rule file):

 # 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"

When examined in the context of 98-kexec.rules, the above change
tests if crash_hotplug is set, and if so, it skips the userspace
initiated unload-then-reload of the crash kernel.

Cpu and memory checks are separated in accordance with
CONFIG_HOTPLUG_CPU and CONFIG_MEMORY_HOTPLUG kernel config options.
If an architecture supports, for example, memory hotplug but not
CPU hotplug, then the /sys/devices/system/memory/crash_hotplug
attribute file is present, but the /sys/devices/system/cpu/crash_hotplug
attribute file will NOT be present. Thus the udev rule will skip
userspace processing of memory hot un/plug events, but the udev
rule will fail for CPU events, thus allowing userspace to process
cpu hot un/plug events (ie the unload-then-reload of the kdump
capture kernel).

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 .../admin-guide/mm/memory-hotplug.rst          |  8 ++++++++
 Documentation/core-api/cpu_hotplug.rst         | 18 ++++++++++++++++++
 drivers/base/cpu.c                             | 14 ++++++++++++++
 drivers/base/memory.c                          | 13 +++++++++++++
 include/linux/kexec.h                          |  8 ++++++++
 5 files changed, 61 insertions(+)

diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index a3c9e8ad8fa0..15fd1751a63c 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -293,6 +293,14 @@ The following files are currently defined:
 		       Availability depends on the CONFIG_ARCH_MEMORY_PROBE
 		       kernel configuration option.
 ``uevent``	       read-write: generic udev file for device subsystems.
+``crash_hotplug``      read-only: when changes to the system memory map
+		       occur due to hot un/plug of memory, this file contains
+		       '1' if the kernel updates the kdump capture kernel memory
+		       map itself (via elfcorehdr), or '0' if userspace must update
+		       the kdump capture kernel memory map.
+
+		       Availability depends on the CONFIG_MEMORY_HOTPLUG kernel
+		       configuration option.
 ====================== =========================================================
 
 .. note::
diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst
index c6f4ba2fb32d..13e33d098645 100644
--- a/Documentation/core-api/cpu_hotplug.rst
+++ b/Documentation/core-api/cpu_hotplug.rst
@@ -750,6 +750,24 @@ will receive all events. A script like::
 
 can process the event further.
 
+When changes to the CPUs in the system occur, the sysfs file
+/sys/devices/system/cpu/crash_hotplug contains '1' if the kernel
+updates the kdump capture kernel list of CPUs itself (via elfcorehdr),
+or '0' if userspace must update the kdump capture kernel list of CPUs.
+
+The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration
+option.
+
+To skip userspace processing of CPU hot un/plug events for kdump
+(ie the unload-then-reload to obtain a current list of CPUs), this sysfs
+file can be used in a udev rule as follows:
+
+ SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
+
+For a cpu hot un/plug event, if the architecture supports kernel updates
+of the elfcorehdr (which contains the list of CPUs), then the rule skips
+the unload-then-reload of the kdump capture kernel.
+
 Kernel Inline Documentations Reference
 ======================================
 
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 4c98849577d4..fedbf87f9d13 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -293,6 +293,17 @@ static ssize_t print_cpus_nohz_full(struct device *dev,
 static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL);
 #endif
 
+#ifdef CONFIG_HOTPLUG_CPU
+#include <linux/kexec.h>
+static ssize_t crash_hotplug_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	return sprintf(buf, "%d\n", crash_hotplug_cpu_support());
+}
+static DEVICE_ATTR_ADMIN_RO(crash_hotplug);
+#endif
+
 static void cpu_device_release(struct device *dev)
 {
 	/*
@@ -469,6 +480,9 @@ static struct attribute *cpu_root_attrs[] = {
 #ifdef CONFIG_NO_HZ_FULL
 	&dev_attr_nohz_full.attr,
 #endif
+#ifdef CONFIG_HOTPLUG_CPU
+	&dev_attr_crash_hotplug.attr,
+#endif
 #ifdef CONFIG_GENERIC_CPU_AUTOPROBE
 	&dev_attr_modalias.attr,
 #endif
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index bc60c9cd3230..b754918c3dac 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -483,6 +483,16 @@ static ssize_t auto_online_blocks_store(struct device *dev,
 
 static DEVICE_ATTR_RW(auto_online_blocks);
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+#include <linux/kexec.h>
+static ssize_t crash_hotplug_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", crash_hotplug_memory_support());
+}
+static DEVICE_ATTR_RO(crash_hotplug);
+#endif
+
 /*
  * Some architectures will have custom drivers to do this, and
  * will not need to do it from userspace.  The fake hot-add code
@@ -887,6 +897,9 @@ static struct attribute *memory_root_attrs[] = {
 
 	&dev_attr_block_size_bytes.attr,
 	&dev_attr_auto_online_blocks.attr,
+#ifdef CONFIG_MEMORY_HOTPLUG
+	&dev_attr_crash_hotplug.attr,
+#endif
 	NULL
 };
 
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 9597b41136ec..a48577a36fb8 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -529,6 +529,14 @@ static inline void arch_crash_handle_hotplug_event(struct kimage *image,
 }
 #endif
 
+#ifndef crash_hotplug_cpu_support
+static inline int crash_hotplug_cpu_support(void) { return 0; }
+#endif
+
+#ifndef crash_hotplug_memory_support
+static inline int crash_hotplug_memory_support(void) { return 0; }
+#endif
+
 #else /* !CONFIG_KEXEC_CORE */
 struct pt_regs;
 struct task_struct;
-- 
2.31.1

[PATCH v11 6/7] crash: memory and cpu hotplug sysfs attributes

[Eric DeVolder]

This introduces the crash_hotplug attribute for memory and CPUs
for use by userspace.  This change directly facilitates the udev
rule for managing userspace re-loading of the crash kernel upon
hot un/plug changes.

For memory, this changeset introduces the crash_hotplug attribute
to the /sys/devices/system/memory directory. For example:

 # udevadm info --attribute-walk /sys/devices/system/memory/memory81
  looking at device '/devices/system/memory/memory81':
    KERNEL=="memory81"
    SUBSYSTEM=="memory"
    DRIVER==""
    ATTR{online}=="1"
    ATTR{phys_device}=="0"
    ATTR{phys_index}=="00000051"
    ATTR{removable}=="1"
    ATTR{state}=="online"
    ATTR{valid_zones}=="Movable"

  looking at parent device '/devices/system/memory':
    KERNELS=="memory"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{auto_online_blocks}=="offline"
    ATTRS{block_size_bytes}=="8000000"
    ATTRS{crash_hotplug}=="1"

For CPUs, this changeset introduces the crash_hotplug attribute
to the /sys/devices/system/cpu directory. For example:

 # udevadm info --attribute-walk /sys/devices/system/cpu/cpu0
  looking at device '/devices/system/cpu/cpu0':
    KERNEL=="cpu0"
    SUBSYSTEM=="cpu"
    DRIVER=="processor"
    ATTR{crash_notes}=="277c38600"
    ATTR{crash_notes_size}=="368"
    ATTR{online}=="1"

  looking at parent device '/devices/system/cpu':
    KERNELS=="cpu"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{crash_hotplug}=="1"
    ATTRS{isolated}==""
    ATTRS{kernel_max}=="8191"
    ATTRS{nohz_full}=="  (null)"
    ATTRS{offline}=="4-7"
    ATTRS{online}=="0-3"
    ATTRS{possible}=="0-7"
    ATTRS{present}=="0-3"

With these sysfs attributes in place, it is possible to efficiently
instruct the udev rule to skip crash kernel reloading.

For example, the following is the proposed udev rule change for RHEL
system 98-kexec.rules (as the first lines of the rule file):

 # 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"

When examined in the context of 98-kexec.rules, the above change
tests if crash_hotplug is set, and if so, it skips the userspace
initiated unload-then-reload of the crash kernel.

Cpu and memory checks are separated in accordance with
CONFIG_HOTPLUG_CPU and CONFIG_MEMORY_HOTPLUG kernel config options.
If an architecture supports, for example, memory hotplug but not
CPU hotplug, then the /sys/devices/system/memory/crash_hotplug
attribute file is present, but the /sys/devices/system/cpu/crash_hotplug
attribute file will NOT be present. Thus the udev rule will skip
userspace processing of memory hot un/plug events, but the udev
rule will fail for CPU events, thus allowing userspace to process
cpu hot un/plug events (ie the unload-then-reload of the kdump
capture kernel).

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 .../admin-guide/mm/memory-hotplug.rst          |  8 ++++++++
 Documentation/core-api/cpu_hotplug.rst         | 18 ++++++++++++++++++
 drivers/base/cpu.c                             | 14 ++++++++++++++
 drivers/base/memory.c                          | 13 +++++++++++++
 include/linux/kexec.h                          |  8 ++++++++
 5 files changed, 61 insertions(+)

diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index a3c9e8ad8fa0..15fd1751a63c 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -293,6 +293,14 @@ The following files are currently defined:
 		       Availability depends on the CONFIG_ARCH_MEMORY_PROBE
 		       kernel configuration option.
 ``uevent``	       read-write: generic udev file for device subsystems.
+``crash_hotplug``      read-only: when changes to the system memory map
+		       occur due to hot un/plug of memory, this file contains
+		       '1' if the kernel updates the kdump capture kernel memory
+		       map itself (via elfcorehdr), or '0' if userspace must update
+		       the kdump capture kernel memory map.
+
+		       Availability depends on the CONFIG_MEMORY_HOTPLUG kernel
+		       configuration option.
 ====================== =========================================================
 
 .. note::
diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst
index c6f4ba2fb32d..13e33d098645 100644
--- a/Documentation/core-api/cpu_hotplug.rst
+++ b/Documentation/core-api/cpu_hotplug.rst
@@ -750,6 +750,24 @@ will receive all events. A script like::
 
 can process the event further.
 
+When changes to the CPUs in the system occur, the sysfs file
+/sys/devices/system/cpu/crash_hotplug contains '1' if the kernel
+updates the kdump capture kernel list of CPUs itself (via elfcorehdr),
+or '0' if userspace must update the kdump capture kernel list of CPUs.
+
+The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration
+option.
+
+To skip userspace processing of CPU hot un/plug events for kdump
+(ie the unload-then-reload to obtain a current list of CPUs), this sysfs
+file can be used in a udev rule as follows:
+
+ SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
+
+For a cpu hot un/plug event, if the architecture supports kernel updates
+of the elfcorehdr (which contains the list of CPUs), then the rule skips
+the unload-then-reload of the kdump capture kernel.
+
 Kernel Inline Documentations Reference
 ======================================
 
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 4c98849577d4..fedbf87f9d13 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -293,6 +293,17 @@ static ssize_t print_cpus_nohz_full(struct device *dev,
 static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL);
 #endif
 
+#ifdef CONFIG_HOTPLUG_CPU
+#include <linux/kexec.h>
+static ssize_t crash_hotplug_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	return sprintf(buf, "%d\n", crash_hotplug_cpu_support());
+}
+static DEVICE_ATTR_ADMIN_RO(crash_hotplug);
+#endif
+
 static void cpu_device_release(struct device *dev)
 {
 	/*
@@ -469,6 +480,9 @@ static struct attribute *cpu_root_attrs[] = {
 #ifdef CONFIG_NO_HZ_FULL
 	&dev_attr_nohz_full.attr,
 #endif
+#ifdef CONFIG_HOTPLUG_CPU
+	&dev_attr_crash_hotplug.attr,
+#endif
 #ifdef CONFIG_GENERIC_CPU_AUTOPROBE
 	&dev_attr_modalias.attr,
 #endif
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index bc60c9cd3230..b754918c3dac 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -483,6 +483,16 @@ static ssize_t auto_online_blocks_store(struct device *dev,
 
 static DEVICE_ATTR_RW(auto_online_blocks);
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+#include <linux/kexec.h>
+static ssize_t crash_hotplug_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", crash_hotplug_memory_support());
+}
+static DEVICE_ATTR_RO(crash_hotplug);
+#endif
+
 /*
  * Some architectures will have custom drivers to do this, and
  * will not need to do it from userspace.  The fake hot-add code
@@ -887,6 +897,9 @@ static struct attribute *memory_root_attrs[] = {
 
 	&dev_attr_block_size_bytes.attr,
 	&dev_attr_auto_online_blocks.attr,
+#ifdef CONFIG_MEMORY_HOTPLUG
+	&dev_attr_crash_hotplug.attr,
+#endif
 	NULL
 };
 
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 9597b41136ec..a48577a36fb8 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -529,6 +529,14 @@ static inline void arch_crash_handle_hotplug_event(struct kimage *image,
 }
 #endif
 
+#ifndef crash_hotplug_cpu_support
+static inline int crash_hotplug_cpu_support(void) { return 0; }
+#endif
+
+#ifndef crash_hotplug_memory_support
+static inline int crash_hotplug_memory_support(void) { return 0; }
+#endif
+
 #else /* !CONFIG_KEXEC_CORE */
 struct pt_regs;
 struct task_struct;
-- 
2.31.1


_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCH v11 7/7] x86/crash: Add x86 crash hotplug support

[Eric DeVolder]

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.

When loading the crash kernel via kexec_load or kexec_file_load,
the elfcorehdr is identified at run time in
crash_core:handle_hotplug_event().

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. The kexec_load is also supported, but also
requires a corresponding change to userspace kexec-tools.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
 arch/x86/Kconfig             |  11 ++++
 arch/x86/include/asm/kexec.h |  20 +++++++
 arch/x86/kernel/crash.c      | 102 +++++++++++++++++++++++++++++++++++
 3 files changed, 133 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f9920f1341c8..cdfc9b2fdf98 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2056,6 +2056,17 @@ 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/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index a3760ca796aa..432073385b2d 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -212,6 +212,26 @@ typedef void crash_vmclear_fn(void);
 extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
 extern void kdump_nmi_shootdown_cpus(void);
 
+void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
+#define arch_map_crash_pages arch_map_crash_pages
+
+void arch_unmap_crash_pages(void **ptr);
+#define arch_unmap_crash_pages arch_unmap_crash_pages
+
+void arch_crash_handle_hotplug_event(struct kimage *image,
+		unsigned int hp_action);
+#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
+
+#ifdef CONFIG_HOTPLUG_CPU
+static inline int crash_hotplug_cpu_support(void) { return 1; }
+#define crash_hotplug_cpu_support crash_hotplug_cpu_support
+#endif
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+static inline int crash_hotplug_memory_support(void) { return 1; }
+#define crash_hotplug_memory_support crash_hotplug_memory_support
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_KEXEC_H */
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9ceb93c176a6..8fc7d678ac72 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>
@@ -397,7 +398,18 @@ 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);
+	/* Mark as usable to crash kernel, else crash kernel fails on boot */
+	image->elf_headers_sz = kbuf.memsz;
+	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);
@@ -412,3 +424,93 @@ int crash_load_segments(struct kimage *image)
 	return ret;
 }
 #endif /* CONFIG_KEXEC_FILE */
+
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+/*
+ * 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 *arch_map_crash_pages(unsigned long paddr, unsigned long size)
+{
+	void *ptr = NULL;
+
+	if (size > 0) {
+		struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
+
+		ptr = kmap_local_page(page);
+	}
+
+	return ptr;
+}
+
+void arch_unmap_crash_pages(void **ptr)
+{
+	if (ptr) {
+		if (*ptr)
+			kunmap_local(*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
+ *
+ * To accurately reflect hot un/plug changes, the new elfcorehdr
+ * is prepared in a kernel buffer, and then it is written on top
+ * of the existing/old elfcorehdr.
+ */
+void arch_crash_handle_hotplug_event(struct kimage *image,
+	unsigned int hp_action)
+{
+	struct kexec_segment *ksegment;
+	unsigned char *ptr = NULL;
+	unsigned long elfsz = 0;
+	void *elfbuf = NULL;
+	unsigned long mem, memsz;
+
+	/*
+	 * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event()
+	 */
+	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;
+	}
+	if (elfsz > memsz) {
+		pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu",
+			elfsz, memsz);
+		goto out;
+	}
+
+	/*
+	 * At this point, we are all but assured of success.
+	 * Copy new elfcorehdr into destination.
+	 */
+	ptr = arch_map_crash_pages(mem, memsz);
+	if (ptr) {
+		/*
+		 * Temporarily invalidate the crash image while the
+		 * elfcorehdr is updated.
+		 */
+		xchg(&kexec_crash_image, NULL);
+		memcpy_flushcache((void *)ptr, elfbuf, elfsz);
+		xchg(&kexec_crash_image, image);
+	}
+	arch_unmap_crash_pages((void **)&ptr);
+	pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
+
+out:
+	if (elfbuf)
+		vfree(elfbuf);
+}
+#endif
-- 
2.31.1

[PATCH v11 7/7] x86/crash: Add x86 crash hotplug support

[Eric DeVolder]

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.

When loading the crash kernel via kexec_load or kexec_file_load,
the elfcorehdr is identified at run time in
crash_core:handle_hotplug_event().

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. The kexec_load is also supported, but also
requires a corresponding change to userspace kexec-tools.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
 arch/x86/Kconfig             |  11 ++++
 arch/x86/include/asm/kexec.h |  20 +++++++
 arch/x86/kernel/crash.c      | 102 +++++++++++++++++++++++++++++++++++
 3 files changed, 133 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f9920f1341c8..cdfc9b2fdf98 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2056,6 +2056,17 @@ 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/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index a3760ca796aa..432073385b2d 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -212,6 +212,26 @@ typedef void crash_vmclear_fn(void);
 extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
 extern void kdump_nmi_shootdown_cpus(void);
 
+void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
+#define arch_map_crash_pages arch_map_crash_pages
+
+void arch_unmap_crash_pages(void **ptr);
+#define arch_unmap_crash_pages arch_unmap_crash_pages
+
+void arch_crash_handle_hotplug_event(struct kimage *image,
+		unsigned int hp_action);
+#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
+
+#ifdef CONFIG_HOTPLUG_CPU
+static inline int crash_hotplug_cpu_support(void) { return 1; }
+#define crash_hotplug_cpu_support crash_hotplug_cpu_support
+#endif
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+static inline int crash_hotplug_memory_support(void) { return 1; }
+#define crash_hotplug_memory_support crash_hotplug_memory_support
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_KEXEC_H */
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9ceb93c176a6..8fc7d678ac72 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>
@@ -397,7 +398,18 @@ 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);
+	/* Mark as usable to crash kernel, else crash kernel fails on boot */
+	image->elf_headers_sz = kbuf.memsz;
+	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);
@@ -412,3 +424,93 @@ int crash_load_segments(struct kimage *image)
 	return ret;
 }
 #endif /* CONFIG_KEXEC_FILE */
+
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+/*
+ * 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 *arch_map_crash_pages(unsigned long paddr, unsigned long size)
+{
+	void *ptr = NULL;
+
+	if (size > 0) {
+		struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
+
+		ptr = kmap_local_page(page);
+	}
+
+	return ptr;
+}
+
+void arch_unmap_crash_pages(void **ptr)
+{
+	if (ptr) {
+		if (*ptr)
+			kunmap_local(*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
+ *
+ * To accurately reflect hot un/plug changes, the new elfcorehdr
+ * is prepared in a kernel buffer, and then it is written on top
+ * of the existing/old elfcorehdr.
+ */
+void arch_crash_handle_hotplug_event(struct kimage *image,
+	unsigned int hp_action)
+{
+	struct kexec_segment *ksegment;
+	unsigned char *ptr = NULL;
+	unsigned long elfsz = 0;
+	void *elfbuf = NULL;
+	unsigned long mem, memsz;
+
+	/*
+	 * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event()
+	 */
+	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;
+	}
+	if (elfsz > memsz) {
+		pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu",
+			elfsz, memsz);
+		goto out;
+	}
+
+	/*
+	 * At this point, we are all but assured of success.
+	 * Copy new elfcorehdr into destination.
+	 */
+	ptr = arch_map_crash_pages(mem, memsz);
+	if (ptr) {
+		/*
+		 * Temporarily invalidate the crash image while the
+		 * elfcorehdr is updated.
+		 */
+		xchg(&kexec_crash_image, NULL);
+		memcpy_flushcache((void *)ptr, elfbuf, elfsz);
+		xchg(&kexec_crash_image, image);
+	}
+	arch_unmap_crash_pages((void **)&ptr);
+	pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
+
+out:
+	if (elfbuf)
+		vfree(elfbuf);
+}
+#endif
-- 
2.31.1


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Re: [PATCH v11 1/7] crash: move crash_prepare_elf64_headers

[Baoquan He]

On 08/26/22 at 01:36pm, Eric DeVolder wrote:
> At the outcome of this patch set, the crash_prepare_elf64_headers()
> is utilized on both the kexec_file_load and kexec_load paths. As
> such, need to move this function out of kexec_file.c and into a
> common location crash_core.c.
> 
> No functionality change.
> 
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>

LGTM,

Baoquan He <bhe@redhat.com>

> ---
>  kernel/crash_core.c | 100 ++++++++++++++++++++++++++++++++++++++++++++
>  kernel/kexec_file.c |  99 -------------------------------------------
>  2 files changed, 100 insertions(+), 99 deletions(-)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 07b26df453a9..8c8c82386e8d 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -10,6 +10,7 @@
>  #include <linux/utsname.h>
>  #include <linux/vmalloc.h>
>  #include <linux/sizes.h>
> +#include <linux/kexec.h>
>  
>  #include <asm/page.h>
>  #include <asm/sections.h>
> @@ -314,6 +315,105 @@ static int __init parse_crashkernel_dummy(char *arg)
>  }
>  early_param("crashkernel", parse_crashkernel_dummy);
>  
> +int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
> +			  void **addr, unsigned long *sz)
> +{
> +	Elf64_Ehdr *ehdr;
> +	Elf64_Phdr *phdr;
> +	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
> +	unsigned char *buf;
> +	unsigned int cpu, i;
> +	unsigned long long notes_addr;
> +	unsigned long mstart, mend;
> +
> +	/* extra phdr for vmcoreinfo ELF note */
> +	nr_phdr = nr_cpus + 1;
> +	nr_phdr += mem->nr_ranges;
> +
> +	/*
> +	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
> +	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
> +	 * I think this is required by tools like gdb. So same physical
> +	 * memory will be mapped in two ELF headers. One will contain kernel
> +	 * text virtual addresses and other will have __va(physical) addresses.
> +	 */
> +
> +	nr_phdr++;
> +	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
> +	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
> +
> +	buf = vzalloc(elf_sz);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	ehdr = (Elf64_Ehdr *)buf;
> +	phdr = (Elf64_Phdr *)(ehdr + 1);
> +	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
> +	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
> +	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
> +	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
> +	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
> +	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
> +	ehdr->e_type = ET_CORE;
> +	ehdr->e_machine = ELF_ARCH;
> +	ehdr->e_version = EV_CURRENT;
> +	ehdr->e_phoff = sizeof(Elf64_Ehdr);
> +	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
> +	ehdr->e_phentsize = sizeof(Elf64_Phdr);
> +
> +	/* Prepare one phdr of type PT_NOTE for each present CPU */
> +	for_each_present_cpu(cpu) {
> +		phdr->p_type = PT_NOTE;
> +		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
> +		phdr->p_offset = phdr->p_paddr = notes_addr;
> +		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
> +		(ehdr->e_phnum)++;
> +		phdr++;
> +	}
> +
> +	/* Prepare one PT_NOTE header for vmcoreinfo */
> +	phdr->p_type = PT_NOTE;
> +	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
> +	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
> +	(ehdr->e_phnum)++;
> +	phdr++;
> +
> +	/* Prepare PT_LOAD type program header for kernel text region */
> +	if (need_kernel_map) {
> +		phdr->p_type = PT_LOAD;
> +		phdr->p_flags = PF_R|PF_W|PF_X;
> +		phdr->p_vaddr = (unsigned long) _text;
> +		phdr->p_filesz = phdr->p_memsz = _end - _text;
> +		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
> +		ehdr->e_phnum++;
> +		phdr++;
> +	}
> +
> +	/* Go through all the ranges in mem->ranges[] and prepare phdr */
> +	for (i = 0; i < mem->nr_ranges; i++) {
> +		mstart = mem->ranges[i].start;
> +		mend = mem->ranges[i].end;
> +
> +		phdr->p_type = PT_LOAD;
> +		phdr->p_flags = PF_R|PF_W|PF_X;
> +		phdr->p_offset  = mstart;
> +
> +		phdr->p_paddr = mstart;
> +		phdr->p_vaddr = (unsigned long) __va(mstart);
> +		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
> +		phdr->p_align = 0;
> +		ehdr->e_phnum++;
> +		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
> +			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
> +			ehdr->e_phnum, phdr->p_offset);
> +		phdr++;
> +	}
> +
> +	*addr = buf;
> +	*sz = elf_sz;
> +	return 0;
> +}
> +
>  Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
>  			  void *data, size_t data_len)
>  {
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 1d546dc97c50..8017eeb43036 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -1217,102 +1217,3 @@ int crash_exclude_mem_range(struct crash_mem *mem,
>  	mem->nr_ranges++;
>  	return 0;
>  }
> -
> -int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
> -			  void **addr, unsigned long *sz)
> -{
> -	Elf64_Ehdr *ehdr;
> -	Elf64_Phdr *phdr;
> -	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
> -	unsigned char *buf;
> -	unsigned int cpu, i;
> -	unsigned long long notes_addr;
> -	unsigned long mstart, mend;
> -
> -	/* extra phdr for vmcoreinfo ELF note */
> -	nr_phdr = nr_cpus + 1;
> -	nr_phdr += mem->nr_ranges;
> -
> -	/*
> -	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
> -	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
> -	 * I think this is required by tools like gdb. So same physical
> -	 * memory will be mapped in two ELF headers. One will contain kernel
> -	 * text virtual addresses and other will have __va(physical) addresses.
> -	 */
> -
> -	nr_phdr++;
> -	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
> -	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
> -
> -	buf = vzalloc(elf_sz);
> -	if (!buf)
> -		return -ENOMEM;
> -
> -	ehdr = (Elf64_Ehdr *)buf;
> -	phdr = (Elf64_Phdr *)(ehdr + 1);
> -	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
> -	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
> -	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
> -	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
> -	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
> -	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
> -	ehdr->e_type = ET_CORE;
> -	ehdr->e_machine = ELF_ARCH;
> -	ehdr->e_version = EV_CURRENT;
> -	ehdr->e_phoff = sizeof(Elf64_Ehdr);
> -	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
> -	ehdr->e_phentsize = sizeof(Elf64_Phdr);
> -
> -	/* Prepare one phdr of type PT_NOTE for each present CPU */
> -	for_each_present_cpu(cpu) {
> -		phdr->p_type = PT_NOTE;
> -		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
> -		phdr->p_offset = phdr->p_paddr = notes_addr;
> -		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
> -		(ehdr->e_phnum)++;
> -		phdr++;
> -	}
> -
> -	/* Prepare one PT_NOTE header for vmcoreinfo */
> -	phdr->p_type = PT_NOTE;
> -	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
> -	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
> -	(ehdr->e_phnum)++;
> -	phdr++;
> -
> -	/* Prepare PT_LOAD type program header for kernel text region */
> -	if (need_kernel_map) {
> -		phdr->p_type = PT_LOAD;
> -		phdr->p_flags = PF_R|PF_W|PF_X;
> -		phdr->p_vaddr = (unsigned long) _text;
> -		phdr->p_filesz = phdr->p_memsz = _end - _text;
> -		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
> -		ehdr->e_phnum++;
> -		phdr++;
> -	}
> -
> -	/* Go through all the ranges in mem->ranges[] and prepare phdr */
> -	for (i = 0; i < mem->nr_ranges; i++) {
> -		mstart = mem->ranges[i].start;
> -		mend = mem->ranges[i].end;
> -
> -		phdr->p_type = PT_LOAD;
> -		phdr->p_flags = PF_R|PF_W|PF_X;
> -		phdr->p_offset  = mstart;
> -
> -		phdr->p_paddr = mstart;
> -		phdr->p_vaddr = (unsigned long) __va(mstart);
> -		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
> -		phdr->p_align = 0;
> -		ehdr->e_phnum++;
> -		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
> -			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
> -			ehdr->e_phnum, phdr->p_offset);
> -		phdr++;
> -	}
> -
> -	*addr = buf;
> -	*sz = elf_sz;
> -	return 0;
> -}
> -- 
> 2.31.1
> 

Re: [PATCH v11 1/7] crash: move crash_prepare_elf64_headers

[Baoquan He]

On 08/26/22 at 01:36pm, Eric DeVolder wrote:
> At the outcome of this patch set, the crash_prepare_elf64_headers()
> is utilized on both the kexec_file_load and kexec_load paths. As
> such, need to move this function out of kexec_file.c and into a
> common location crash_core.c.
> 
> No functionality change.
> 
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>

LGTM,

Baoquan He <bhe@redhat.com>

> ---
>  kernel/crash_core.c | 100 ++++++++++++++++++++++++++++++++++++++++++++
>  kernel/kexec_file.c |  99 -------------------------------------------
>  2 files changed, 100 insertions(+), 99 deletions(-)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 07b26df453a9..8c8c82386e8d 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -10,6 +10,7 @@
>  #include <linux/utsname.h>
>  #include <linux/vmalloc.h>
>  #include <linux/sizes.h>
> +#include <linux/kexec.h>
>  
>  #include <asm/page.h>
>  #include <asm/sections.h>
> @@ -314,6 +315,105 @@ static int __init parse_crashkernel_dummy(char *arg)
>  }
>  early_param("crashkernel", parse_crashkernel_dummy);
>  
> +int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
> +			  void **addr, unsigned long *sz)
> +{
> +	Elf64_Ehdr *ehdr;
> +	Elf64_Phdr *phdr;
> +	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
> +	unsigned char *buf;
> +	unsigned int cpu, i;
> +	unsigned long long notes_addr;
> +	unsigned long mstart, mend;
> +
> +	/* extra phdr for vmcoreinfo ELF note */
> +	nr_phdr = nr_cpus + 1;
> +	nr_phdr += mem->nr_ranges;
> +
> +	/*
> +	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
> +	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
> +	 * I think this is required by tools like gdb. So same physical
> +	 * memory will be mapped in two ELF headers. One will contain kernel
> +	 * text virtual addresses and other will have __va(physical) addresses.
> +	 */
> +
> +	nr_phdr++;
> +	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
> +	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
> +
> +	buf = vzalloc(elf_sz);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	ehdr = (Elf64_Ehdr *)buf;
> +	phdr = (Elf64_Phdr *)(ehdr + 1);
> +	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
> +	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
> +	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
> +	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
> +	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
> +	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
> +	ehdr->e_type = ET_CORE;
> +	ehdr->e_machine = ELF_ARCH;
> +	ehdr->e_version = EV_CURRENT;
> +	ehdr->e_phoff = sizeof(Elf64_Ehdr);
> +	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
> +	ehdr->e_phentsize = sizeof(Elf64_Phdr);
> +
> +	/* Prepare one phdr of type PT_NOTE for each present CPU */
> +	for_each_present_cpu(cpu) {
> +		phdr->p_type = PT_NOTE;
> +		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
> +		phdr->p_offset = phdr->p_paddr = notes_addr;
> +		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
> +		(ehdr->e_phnum)++;
> +		phdr++;
> +	}
> +
> +	/* Prepare one PT_NOTE header for vmcoreinfo */
> +	phdr->p_type = PT_NOTE;
> +	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
> +	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
> +	(ehdr->e_phnum)++;
> +	phdr++;
> +
> +	/* Prepare PT_LOAD type program header for kernel text region */
> +	if (need_kernel_map) {
> +		phdr->p_type = PT_LOAD;
> +		phdr->p_flags = PF_R|PF_W|PF_X;
> +		phdr->p_vaddr = (unsigned long) _text;
> +		phdr->p_filesz = phdr->p_memsz = _end - _text;
> +		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
> +		ehdr->e_phnum++;
> +		phdr++;
> +	}
> +
> +	/* Go through all the ranges in mem->ranges[] and prepare phdr */
> +	for (i = 0; i < mem->nr_ranges; i++) {
> +		mstart = mem->ranges[i].start;
> +		mend = mem->ranges[i].end;
> +
> +		phdr->p_type = PT_LOAD;
> +		phdr->p_flags = PF_R|PF_W|PF_X;
> +		phdr->p_offset  = mstart;
> +
> +		phdr->p_paddr = mstart;
> +		phdr->p_vaddr = (unsigned long) __va(mstart);
> +		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
> +		phdr->p_align = 0;
> +		ehdr->e_phnum++;
> +		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
> +			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
> +			ehdr->e_phnum, phdr->p_offset);
> +		phdr++;
> +	}
> +
> +	*addr = buf;
> +	*sz = elf_sz;
> +	return 0;
> +}
> +
>  Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
>  			  void *data, size_t data_len)
>  {
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 1d546dc97c50..8017eeb43036 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -1217,102 +1217,3 @@ int crash_exclude_mem_range(struct crash_mem *mem,
>  	mem->nr_ranges++;
>  	return 0;
>  }
> -
> -int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
> -			  void **addr, unsigned long *sz)
> -{
> -	Elf64_Ehdr *ehdr;
> -	Elf64_Phdr *phdr;
> -	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
> -	unsigned char *buf;
> -	unsigned int cpu, i;
> -	unsigned long long notes_addr;
> -	unsigned long mstart, mend;
> -
> -	/* extra phdr for vmcoreinfo ELF note */
> -	nr_phdr = nr_cpus + 1;
> -	nr_phdr += mem->nr_ranges;
> -
> -	/*
> -	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
> -	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
> -	 * I think this is required by tools like gdb. So same physical
> -	 * memory will be mapped in two ELF headers. One will contain kernel
> -	 * text virtual addresses and other will have __va(physical) addresses.
> -	 */
> -
> -	nr_phdr++;
> -	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
> -	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
> -
> -	buf = vzalloc(elf_sz);
> -	if (!buf)
> -		return -ENOMEM;
> -
> -	ehdr = (Elf64_Ehdr *)buf;
> -	phdr = (Elf64_Phdr *)(ehdr + 1);
> -	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
> -	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
> -	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
> -	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
> -	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
> -	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
> -	ehdr->e_type = ET_CORE;
> -	ehdr->e_machine = ELF_ARCH;
> -	ehdr->e_version = EV_CURRENT;
> -	ehdr->e_phoff = sizeof(Elf64_Ehdr);
> -	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
> -	ehdr->e_phentsize = sizeof(Elf64_Phdr);
> -
> -	/* Prepare one phdr of type PT_NOTE for each present CPU */
> -	for_each_present_cpu(cpu) {
> -		phdr->p_type = PT_NOTE;
> -		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
> -		phdr->p_offset = phdr->p_paddr = notes_addr;
> -		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
> -		(ehdr->e_phnum)++;
> -		phdr++;
> -	}
> -
> -	/* Prepare one PT_NOTE header for vmcoreinfo */
> -	phdr->p_type = PT_NOTE;
> -	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
> -	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
> -	(ehdr->e_phnum)++;
> -	phdr++;
> -
> -	/* Prepare PT_LOAD type program header for kernel text region */
> -	if (need_kernel_map) {
> -		phdr->p_type = PT_LOAD;
> -		phdr->p_flags = PF_R|PF_W|PF_X;
> -		phdr->p_vaddr = (unsigned long) _text;
> -		phdr->p_filesz = phdr->p_memsz = _end - _text;
> -		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
> -		ehdr->e_phnum++;
> -		phdr++;
> -	}
> -
> -	/* Go through all the ranges in mem->ranges[] and prepare phdr */
> -	for (i = 0; i < mem->nr_ranges; i++) {
> -		mstart = mem->ranges[i].start;
> -		mend = mem->ranges[i].end;
> -
> -		phdr->p_type = PT_LOAD;
> -		phdr->p_flags = PF_R|PF_W|PF_X;
> -		phdr->p_offset  = mstart;
> -
> -		phdr->p_paddr = mstart;
> -		phdr->p_vaddr = (unsigned long) __va(mstart);
> -		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
> -		phdr->p_align = 0;
> -		ehdr->e_phnum++;
> -		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
> -			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
> -			ehdr->e_phnum, phdr->p_offset);
> -		phdr++;
> -	}
> -
> -	*addr = buf;
> -	*sz = elf_sz;
> -	return 0;
> -}
> -- 
> 2.31.1
> 


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Re: [PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support

[Baoquan He]

On 08/26/22 at 01:37pm, Eric DeVolder wrote:
> CPU and memory change notifications are received in order to
> regenerate the elfcorehdr.
> 
> To support cpu hotplug, a callback is registered to capture the
> CPUHP_AP_ONLINE_DYN online and offline events via
> cpuhp_setup_state_nocalls().
> 
> To support memory hotplug, a notifier is registered to capture the
> MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
> 
> The cpu callback and memory notifiers call handle_hotplug_event()
> which performs needed tasks and then dispatches the event to the
> architecture specific arch_crash_handle_hotplug_event(). During the
> process, the kexec_mutex is held.
> 
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> ---
>  include/linux/crash_core.h |   8 +++
>  include/linux/kexec.h      |  26 +++++++
>  kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 168 insertions(+)
> 
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index de62a722431e..3b99e69b011f 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
>  int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
>  		unsigned long long *crash_size, unsigned long long *crash_base);
>  
> +#define KEXEC_CRASH_HP_REMOVE_CPU		0
> +#define KEXEC_CRASH_HP_ADD_CPU			1
> +#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
                                        ~~
                                        Nitpick, These arenot aligned, 
> +#define KEXEC_CRASH_HP_ADD_MEMORY		3
> +#define KEXEC_CRASH_HP_INVALID_CPU		-1U
> +
> +struct kimage;
> +
>  #endif /* LINUX_CRASH_CORE_H */
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 4eefa631e0ae..9597b41136ec 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -374,6 +374,13 @@ struct kimage {
>  	struct purgatory_info purgatory_info;
>  #endif
>  
> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> +	bool hotplug_event;
> +	unsigned int offlinecpu;
> +	bool elfcorehdr_index_valid;
> +	int elfcorehdr_index;
> +#endif
> +
>  #ifdef CONFIG_IMA_KEXEC
>  	/* Virtual address of IMA measurement buffer for kexec syscall */
>  	void *ima_buffer;
> @@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
>  static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
>  #endif
>  
> +#ifndef arch_map_crash_pages
> +static inline void *arch_map_crash_pages(unsigned long paddr,
> +		unsigned long size)
> +{
> +	return NULL;
> +}
> +#endif
> +
> +#ifndef arch_unmap_crash_pages
> +static inline void arch_unmap_crash_pages(void **ptr) { }
> +#endif
> +
> +#ifndef arch_crash_handle_hotplug_event
> +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
> +		unsigned int hp_action)
> +{
> +}
> +#endif
> +
>  #else /* !CONFIG_KEXEC_CORE */
>  struct pt_regs;
>  struct task_struct;
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 0f8aa659cca4..455150205ded 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -11,6 +11,8 @@
>  #include <linux/vmalloc.h>
>  #include <linux/sizes.h>
>  #include <linux/kexec.h>
> +#include <linux/memory.h>
> +#include <linux/cpuhotplug.h>
>  
>  #include <asm/page.h>
>  #include <asm/sections.h>
> @@ -18,6 +20,7 @@
>  #include <crypto/sha1.h>
>  
>  #include "kallsyms_internal.h"
> +#include "kexec_internal.h"
>  
>  /* vmcoreinfo stuff */
>  unsigned char *vmcoreinfo_data;
> @@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
>  }
>  
>  subsys_initcall(crash_save_vmcoreinfo_init);
> +
> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> +/*
> + * 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.
> + *
> + * In order to make changes to elfcorehdr, two conditions are needed:
> + * First, the segment containing the elfcorehdr must be large enough
> + * to permit a growing number of resources. The elfcorehdr memory is
> + * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
> + * 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).
> + */
> +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
> +{
> +	/* Obtain lock while changing crash information */
> +	mutex_lock(&kexec_mutex);
> +
> +	/* Check kdump is loaded */
> +	if (kexec_crash_image) {
> +		struct kimage *image = kexec_crash_image;
> +
> +		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
> +			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
> +			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
> +		else
> +			pr_debug("crash hp: hp_action %u", hp_action);
                                                       ^~ "\n" missed
> +		/*
> +		 * When the struct kimage is alloced, it is wiped to zero, so
                                             ~~~~ alloced is confusing, s/alloced/allocated/
                                            We can accept alloc being used, alloced is a little weird.
> +		 * the elfcorehdr_index_valid defaults to false. Find the
> +		 * segment containing the elfcorehdr, if not already found.
> +		 * This works for both the kexec_load and kexec_file_load paths.
> +		 */
> +		if (!image->elfcorehdr_index_valid) {
> +			unsigned char *ptr;
> +			unsigned long mem, memsz;
> +			unsigned int n;
> +
> +			for (n = 0; n < image->nr_segments; n++) {
> +				mem = image->segment[n].mem;
> +				memsz = image->segment[n].memsz;
> +				ptr = arch_map_crash_pages(mem, memsz);
OK, I see. You want to avoid the over 80 chars line, so introducing
two local variables. We may be able to tolerate that in this case. No
strong opinion, let's see if other people have concern about it.

Other than these nitpicks, this patch looks good to me.
Acked-by: Baoquan He <bhe@redhat.com>

> +				if (ptr) {
> +					/* The segment containing elfcorehdr */
> +					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
> +						image->elfcorehdr_index = (int)n;
> +						image->elfcorehdr_index_valid = true;
> +					}
> +				}
> +				arch_unmap_crash_pages((void **)&ptr);
> +			}
> +		}
> +
> +		if (!image->elfcorehdr_index_valid) {
> +			pr_err("crash hp: unable to locate elfcorehdr segment");
> +			goto out;
> +		}
> +
> +		/* Needed in order for the segments to be updated */
> +		arch_kexec_unprotect_crashkres();
> +
> +		/* Flag to differentiate between normal load and hotplug */
> +		image->hotplug_event = true;
> +
> +		/* Now invoke arch-specific update handler */
> +		arch_crash_handle_hotplug_event(image, hp_action);
> +
> +		/* No longer handling a hotplug event */
> +		image->hotplug_event = false;
> +
> +		/* Change back to read-only */
> +		arch_kexec_protect_crashkres();
> +	}
> +
> +out:
> +	/* Release lock now that update complete */
> +	mutex_unlock(&kexec_mutex);
> +}
> +
> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
> +{
> +	switch (val) {
> +	case MEM_ONLINE:
> +		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
> +		break;
> +
> +	case MEM_OFFLINE:
> +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
> +		break;
> +	}
> +	return NOTIFY_OK;
> +}
> +
> +static struct notifier_block crash_memhp_nb = {
> +	.notifier_call = crash_memhp_notifier,
> +	.priority = 0
> +};
> +
> +static int crash_cpuhp_online(unsigned int cpu)
> +{
> +	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
> +	return 0;
> +}
> +
> +static int crash_cpuhp_offline(unsigned int cpu)
> +{
> +	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
> +	return 0;
> +}
> +
> +static int __init crash_hotplug_init(void)
> +{
> +	int result = 0;
> +
> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> +		register_memory_notifier(&crash_memhp_nb);
> +
> +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
> +		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> +						   "crash/cpuhp",
> +						   crash_cpuhp_online,
> +						   crash_cpuhp_offline);
> +
> +	return result;
> +}
> +
> +subsys_initcall(crash_hotplug_init);
> +#endif
> -- 
> 2.31.1
> 

Re: [PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support

[Baoquan He]

On 08/26/22 at 01:37pm, Eric DeVolder wrote:
> CPU and memory change notifications are received in order to
> regenerate the elfcorehdr.
> 
> To support cpu hotplug, a callback is registered to capture the
> CPUHP_AP_ONLINE_DYN online and offline events via
> cpuhp_setup_state_nocalls().
> 
> To support memory hotplug, a notifier is registered to capture the
> MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
> 
> The cpu callback and memory notifiers call handle_hotplug_event()
> which performs needed tasks and then dispatches the event to the
> architecture specific arch_crash_handle_hotplug_event(). During the
> process, the kexec_mutex is held.
> 
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> ---
>  include/linux/crash_core.h |   8 +++
>  include/linux/kexec.h      |  26 +++++++
>  kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 168 insertions(+)
> 
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index de62a722431e..3b99e69b011f 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
>  int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
>  		unsigned long long *crash_size, unsigned long long *crash_base);
>  
> +#define KEXEC_CRASH_HP_REMOVE_CPU		0
> +#define KEXEC_CRASH_HP_ADD_CPU			1
> +#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
                                        ~~
                                        Nitpick, These arenot aligned, 
> +#define KEXEC_CRASH_HP_ADD_MEMORY		3
> +#define KEXEC_CRASH_HP_INVALID_CPU		-1U
> +
> +struct kimage;
> +
>  #endif /* LINUX_CRASH_CORE_H */
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 4eefa631e0ae..9597b41136ec 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -374,6 +374,13 @@ struct kimage {
>  	struct purgatory_info purgatory_info;
>  #endif
>  
> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> +	bool hotplug_event;
> +	unsigned int offlinecpu;
> +	bool elfcorehdr_index_valid;
> +	int elfcorehdr_index;
> +#endif
> +
>  #ifdef CONFIG_IMA_KEXEC
>  	/* Virtual address of IMA measurement buffer for kexec syscall */
>  	void *ima_buffer;
> @@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
>  static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
>  #endif
>  
> +#ifndef arch_map_crash_pages
> +static inline void *arch_map_crash_pages(unsigned long paddr,
> +		unsigned long size)
> +{
> +	return NULL;
> +}
> +#endif
> +
> +#ifndef arch_unmap_crash_pages
> +static inline void arch_unmap_crash_pages(void **ptr) { }
> +#endif
> +
> +#ifndef arch_crash_handle_hotplug_event
> +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
> +		unsigned int hp_action)
> +{
> +}
> +#endif
> +
>  #else /* !CONFIG_KEXEC_CORE */
>  struct pt_regs;
>  struct task_struct;
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 0f8aa659cca4..455150205ded 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -11,6 +11,8 @@
>  #include <linux/vmalloc.h>
>  #include <linux/sizes.h>
>  #include <linux/kexec.h>
> +#include <linux/memory.h>
> +#include <linux/cpuhotplug.h>
>  
>  #include <asm/page.h>
>  #include <asm/sections.h>
> @@ -18,6 +20,7 @@
>  #include <crypto/sha1.h>
>  
>  #include "kallsyms_internal.h"
> +#include "kexec_internal.h"
>  
>  /* vmcoreinfo stuff */
>  unsigned char *vmcoreinfo_data;
> @@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
>  }
>  
>  subsys_initcall(crash_save_vmcoreinfo_init);
> +
> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> +/*
> + * 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.
> + *
> + * In order to make changes to elfcorehdr, two conditions are needed:
> + * First, the segment containing the elfcorehdr must be large enough
> + * to permit a growing number of resources. The elfcorehdr memory is
> + * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
> + * 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).
> + */
> +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
> +{
> +	/* Obtain lock while changing crash information */
> +	mutex_lock(&kexec_mutex);
> +
> +	/* Check kdump is loaded */
> +	if (kexec_crash_image) {
> +		struct kimage *image = kexec_crash_image;
> +
> +		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
> +			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
> +			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
> +		else
> +			pr_debug("crash hp: hp_action %u", hp_action);
                                                       ^~ "\n" missed
> +		/*
> +		 * When the struct kimage is alloced, it is wiped to zero, so
                                             ~~~~ alloced is confusing, s/alloced/allocated/
                                            We can accept alloc being used, alloced is a little weird.
> +		 * the elfcorehdr_index_valid defaults to false. Find the
> +		 * segment containing the elfcorehdr, if not already found.
> +		 * This works for both the kexec_load and kexec_file_load paths.
> +		 */
> +		if (!image->elfcorehdr_index_valid) {
> +			unsigned char *ptr;
> +			unsigned long mem, memsz;
> +			unsigned int n;
> +
> +			for (n = 0; n < image->nr_segments; n++) {
> +				mem = image->segment[n].mem;
> +				memsz = image->segment[n].memsz;
> +				ptr = arch_map_crash_pages(mem, memsz);
OK, I see. You want to avoid the over 80 chars line, so introducing
two local variables. We may be able to tolerate that in this case. No
strong opinion, let's see if other people have concern about it.

Other than these nitpicks, this patch looks good to me.
Acked-by: Baoquan He <bhe@redhat.com>

> +				if (ptr) {
> +					/* The segment containing elfcorehdr */
> +					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
> +						image->elfcorehdr_index = (int)n;
> +						image->elfcorehdr_index_valid = true;
> +					}
> +				}
> +				arch_unmap_crash_pages((void **)&ptr);
> +			}
> +		}
> +
> +		if (!image->elfcorehdr_index_valid) {
> +			pr_err("crash hp: unable to locate elfcorehdr segment");
> +			goto out;
> +		}
> +
> +		/* Needed in order for the segments to be updated */
> +		arch_kexec_unprotect_crashkres();
> +
> +		/* Flag to differentiate between normal load and hotplug */
> +		image->hotplug_event = true;
> +
> +		/* Now invoke arch-specific update handler */
> +		arch_crash_handle_hotplug_event(image, hp_action);
> +
> +		/* No longer handling a hotplug event */
> +		image->hotplug_event = false;
> +
> +		/* Change back to read-only */
> +		arch_kexec_protect_crashkres();
> +	}
> +
> +out:
> +	/* Release lock now that update complete */
> +	mutex_unlock(&kexec_mutex);
> +}
> +
> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
> +{
> +	switch (val) {
> +	case MEM_ONLINE:
> +		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
> +		break;
> +
> +	case MEM_OFFLINE:
> +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
> +		break;
> +	}
> +	return NOTIFY_OK;
> +}
> +
> +static struct notifier_block crash_memhp_nb = {
> +	.notifier_call = crash_memhp_notifier,
> +	.priority = 0
> +};
> +
> +static int crash_cpuhp_online(unsigned int cpu)
> +{
> +	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
> +	return 0;
> +}
> +
> +static int crash_cpuhp_offline(unsigned int cpu)
> +{
> +	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
> +	return 0;
> +}
> +
> +static int __init crash_hotplug_init(void)
> +{
> +	int result = 0;
> +
> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> +		register_memory_notifier(&crash_memhp_nb);
> +
> +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
> +		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> +						   "crash/cpuhp",
> +						   crash_cpuhp_online,
> +						   crash_cpuhp_offline);
> +
> +	return result;
> +}
> +
> +subsys_initcall(crash_hotplug_init);
> +#endif
> -- 
> 2.31.1
> 


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Re: [PATCH v11 1/7] crash: move crash_prepare_elf64_headers

[Eric DeVolder]

On 8/30/22 21:50, Baoquan He wrote:
> On 08/26/22 at 01:36pm, Eric DeVolder wrote:
>> At the outcome of this patch set, the crash_prepare_elf64_headers()
>> is utilized on both the kexec_file_load and kexec_load paths. As
>> such, need to move this function out of kexec_file.c and into a
>> common location crash_core.c.
>>
>> No functionality change.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> 
> LGTM,
> 
> Baoquan He <bhe@redhat.com>

Thank you! I'll record that as Acked-by, unless you tell me otherwise.
eric

> 
>> ---
>>   kernel/crash_core.c | 100 ++++++++++++++++++++++++++++++++++++++++++++
>>   kernel/kexec_file.c |  99 -------------------------------------------
>>   2 files changed, 100 insertions(+), 99 deletions(-)
>>
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 07b26df453a9..8c8c82386e8d 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -10,6 +10,7 @@
>>   #include <linux/utsname.h>
>>   #include <linux/vmalloc.h>
>>   #include <linux/sizes.h>
>> +#include <linux/kexec.h>
>>   
>>   #include <asm/page.h>
>>   #include <asm/sections.h>
>> @@ -314,6 +315,105 @@ static int __init parse_crashkernel_dummy(char *arg)
>>   }
>>   early_param("crashkernel", parse_crashkernel_dummy);
>>   
>> +int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
>> +			  void **addr, unsigned long *sz)
>> +{
>> +	Elf64_Ehdr *ehdr;
>> +	Elf64_Phdr *phdr;
>> +	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
>> +	unsigned char *buf;
>> +	unsigned int cpu, i;
>> +	unsigned long long notes_addr;
>> +	unsigned long mstart, mend;
>> +
>> +	/* extra phdr for vmcoreinfo ELF note */
>> +	nr_phdr = nr_cpus + 1;
>> +	nr_phdr += mem->nr_ranges;
>> +
>> +	/*
>> +	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
>> +	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
>> +	 * I think this is required by tools like gdb. So same physical
>> +	 * memory will be mapped in two ELF headers. One will contain kernel
>> +	 * text virtual addresses and other will have __va(physical) addresses.
>> +	 */
>> +
>> +	nr_phdr++;
>> +	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
>> +	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
>> +
>> +	buf = vzalloc(elf_sz);
>> +	if (!buf)
>> +		return -ENOMEM;
>> +
>> +	ehdr = (Elf64_Ehdr *)buf;
>> +	phdr = (Elf64_Phdr *)(ehdr + 1);
>> +	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
>> +	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
>> +	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
>> +	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
>> +	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
>> +	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
>> +	ehdr->e_type = ET_CORE;
>> +	ehdr->e_machine = ELF_ARCH;
>> +	ehdr->e_version = EV_CURRENT;
>> +	ehdr->e_phoff = sizeof(Elf64_Ehdr);
>> +	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
>> +	ehdr->e_phentsize = sizeof(Elf64_Phdr);
>> +
>> +	/* Prepare one phdr of type PT_NOTE for each present CPU */
>> +	for_each_present_cpu(cpu) {
>> +		phdr->p_type = PT_NOTE;
>> +		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
>> +		phdr->p_offset = phdr->p_paddr = notes_addr;
>> +		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
>> +		(ehdr->e_phnum)++;
>> +		phdr++;
>> +	}
>> +
>> +	/* Prepare one PT_NOTE header for vmcoreinfo */
>> +	phdr->p_type = PT_NOTE;
>> +	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
>> +	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
>> +	(ehdr->e_phnum)++;
>> +	phdr++;
>> +
>> +	/* Prepare PT_LOAD type program header for kernel text region */
>> +	if (need_kernel_map) {
>> +		phdr->p_type = PT_LOAD;
>> +		phdr->p_flags = PF_R|PF_W|PF_X;
>> +		phdr->p_vaddr = (unsigned long) _text;
>> +		phdr->p_filesz = phdr->p_memsz = _end - _text;
>> +		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
>> +		ehdr->e_phnum++;
>> +		phdr++;
>> +	}
>> +
>> +	/* Go through all the ranges in mem->ranges[] and prepare phdr */
>> +	for (i = 0; i < mem->nr_ranges; i++) {
>> +		mstart = mem->ranges[i].start;
>> +		mend = mem->ranges[i].end;
>> +
>> +		phdr->p_type = PT_LOAD;
>> +		phdr->p_flags = PF_R|PF_W|PF_X;
>> +		phdr->p_offset  = mstart;
>> +
>> +		phdr->p_paddr = mstart;
>> +		phdr->p_vaddr = (unsigned long) __va(mstart);
>> +		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
>> +		phdr->p_align = 0;
>> +		ehdr->e_phnum++;
>> +		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
>> +			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
>> +			ehdr->e_phnum, phdr->p_offset);
>> +		phdr++;
>> +	}
>> +
>> +	*addr = buf;
>> +	*sz = elf_sz;
>> +	return 0;
>> +}
>> +
>>   Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
>>   			  void *data, size_t data_len)
>>   {
>> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
>> index 1d546dc97c50..8017eeb43036 100644
>> --- a/kernel/kexec_file.c
>> +++ b/kernel/kexec_file.c
>> @@ -1217,102 +1217,3 @@ int crash_exclude_mem_range(struct crash_mem *mem,
>>   	mem->nr_ranges++;
>>   	return 0;
>>   }
>> -
>> -int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
>> -			  void **addr, unsigned long *sz)
>> -{
>> -	Elf64_Ehdr *ehdr;
>> -	Elf64_Phdr *phdr;
>> -	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
>> -	unsigned char *buf;
>> -	unsigned int cpu, i;
>> -	unsigned long long notes_addr;
>> -	unsigned long mstart, mend;
>> -
>> -	/* extra phdr for vmcoreinfo ELF note */
>> -	nr_phdr = nr_cpus + 1;
>> -	nr_phdr += mem->nr_ranges;
>> -
>> -	/*
>> -	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
>> -	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
>> -	 * I think this is required by tools like gdb. So same physical
>> -	 * memory will be mapped in two ELF headers. One will contain kernel
>> -	 * text virtual addresses and other will have __va(physical) addresses.
>> -	 */
>> -
>> -	nr_phdr++;
>> -	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
>> -	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
>> -
>> -	buf = vzalloc(elf_sz);
>> -	if (!buf)
>> -		return -ENOMEM;
>> -
>> -	ehdr = (Elf64_Ehdr *)buf;
>> -	phdr = (Elf64_Phdr *)(ehdr + 1);
>> -	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
>> -	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
>> -	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
>> -	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
>> -	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
>> -	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
>> -	ehdr->e_type = ET_CORE;
>> -	ehdr->e_machine = ELF_ARCH;
>> -	ehdr->e_version = EV_CURRENT;
>> -	ehdr->e_phoff = sizeof(Elf64_Ehdr);
>> -	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
>> -	ehdr->e_phentsize = sizeof(Elf64_Phdr);
>> -
>> -	/* Prepare one phdr of type PT_NOTE for each present CPU */
>> -	for_each_present_cpu(cpu) {
>> -		phdr->p_type = PT_NOTE;
>> -		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
>> -		phdr->p_offset = phdr->p_paddr = notes_addr;
>> -		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
>> -		(ehdr->e_phnum)++;
>> -		phdr++;
>> -	}
>> -
>> -	/* Prepare one PT_NOTE header for vmcoreinfo */
>> -	phdr->p_type = PT_NOTE;
>> -	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
>> -	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
>> -	(ehdr->e_phnum)++;
>> -	phdr++;
>> -
>> -	/* Prepare PT_LOAD type program header for kernel text region */
>> -	if (need_kernel_map) {
>> -		phdr->p_type = PT_LOAD;
>> -		phdr->p_flags = PF_R|PF_W|PF_X;
>> -		phdr->p_vaddr = (unsigned long) _text;
>> -		phdr->p_filesz = phdr->p_memsz = _end - _text;
>> -		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
>> -		ehdr->e_phnum++;
>> -		phdr++;
>> -	}
>> -
>> -	/* Go through all the ranges in mem->ranges[] and prepare phdr */
>> -	for (i = 0; i < mem->nr_ranges; i++) {
>> -		mstart = mem->ranges[i].start;
>> -		mend = mem->ranges[i].end;
>> -
>> -		phdr->p_type = PT_LOAD;
>> -		phdr->p_flags = PF_R|PF_W|PF_X;
>> -		phdr->p_offset  = mstart;
>> -
>> -		phdr->p_paddr = mstart;
>> -		phdr->p_vaddr = (unsigned long) __va(mstart);
>> -		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
>> -		phdr->p_align = 0;
>> -		ehdr->e_phnum++;
>> -		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
>> -			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
>> -			ehdr->e_phnum, phdr->p_offset);
>> -		phdr++;
>> -	}
>> -
>> -	*addr = buf;
>> -	*sz = elf_sz;
>> -	return 0;
>> -}
>> -- 
>> 2.31.1
>>
> 

Re: [PATCH v11 1/7] crash: move crash_prepare_elf64_headers

[Eric DeVolder]

On 8/30/22 21:50, Baoquan He wrote:
> On 08/26/22 at 01:36pm, Eric DeVolder wrote:
>> At the outcome of this patch set, the crash_prepare_elf64_headers()
>> is utilized on both the kexec_file_load and kexec_load paths. As
>> such, need to move this function out of kexec_file.c and into a
>> common location crash_core.c.
>>
>> No functionality change.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> 
> LGTM,
> 
> Baoquan He <bhe@redhat.com>

Thank you! I'll record that as Acked-by, unless you tell me otherwise.
eric

> 
>> ---
>>   kernel/crash_core.c | 100 ++++++++++++++++++++++++++++++++++++++++++++
>>   kernel/kexec_file.c |  99 -------------------------------------------
>>   2 files changed, 100 insertions(+), 99 deletions(-)
>>
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 07b26df453a9..8c8c82386e8d 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -10,6 +10,7 @@
>>   #include <linux/utsname.h>
>>   #include <linux/vmalloc.h>
>>   #include <linux/sizes.h>
>> +#include <linux/kexec.h>
>>   
>>   #include <asm/page.h>
>>   #include <asm/sections.h>
>> @@ -314,6 +315,105 @@ static int __init parse_crashkernel_dummy(char *arg)
>>   }
>>   early_param("crashkernel", parse_crashkernel_dummy);
>>   
>> +int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
>> +			  void **addr, unsigned long *sz)
>> +{
>> +	Elf64_Ehdr *ehdr;
>> +	Elf64_Phdr *phdr;
>> +	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
>> +	unsigned char *buf;
>> +	unsigned int cpu, i;
>> +	unsigned long long notes_addr;
>> +	unsigned long mstart, mend;
>> +
>> +	/* extra phdr for vmcoreinfo ELF note */
>> +	nr_phdr = nr_cpus + 1;
>> +	nr_phdr += mem->nr_ranges;
>> +
>> +	/*
>> +	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
>> +	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
>> +	 * I think this is required by tools like gdb. So same physical
>> +	 * memory will be mapped in two ELF headers. One will contain kernel
>> +	 * text virtual addresses and other will have __va(physical) addresses.
>> +	 */
>> +
>> +	nr_phdr++;
>> +	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
>> +	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
>> +
>> +	buf = vzalloc(elf_sz);
>> +	if (!buf)
>> +		return -ENOMEM;
>> +
>> +	ehdr = (Elf64_Ehdr *)buf;
>> +	phdr = (Elf64_Phdr *)(ehdr + 1);
>> +	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
>> +	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
>> +	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
>> +	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
>> +	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
>> +	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
>> +	ehdr->e_type = ET_CORE;
>> +	ehdr->e_machine = ELF_ARCH;
>> +	ehdr->e_version = EV_CURRENT;
>> +	ehdr->e_phoff = sizeof(Elf64_Ehdr);
>> +	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
>> +	ehdr->e_phentsize = sizeof(Elf64_Phdr);
>> +
>> +	/* Prepare one phdr of type PT_NOTE for each present CPU */
>> +	for_each_present_cpu(cpu) {
>> +		phdr->p_type = PT_NOTE;
>> +		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
>> +		phdr->p_offset = phdr->p_paddr = notes_addr;
>> +		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
>> +		(ehdr->e_phnum)++;
>> +		phdr++;
>> +	}
>> +
>> +	/* Prepare one PT_NOTE header for vmcoreinfo */
>> +	phdr->p_type = PT_NOTE;
>> +	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
>> +	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
>> +	(ehdr->e_phnum)++;
>> +	phdr++;
>> +
>> +	/* Prepare PT_LOAD type program header for kernel text region */
>> +	if (need_kernel_map) {
>> +		phdr->p_type = PT_LOAD;
>> +		phdr->p_flags = PF_R|PF_W|PF_X;
>> +		phdr->p_vaddr = (unsigned long) _text;
>> +		phdr->p_filesz = phdr->p_memsz = _end - _text;
>> +		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
>> +		ehdr->e_phnum++;
>> +		phdr++;
>> +	}
>> +
>> +	/* Go through all the ranges in mem->ranges[] and prepare phdr */
>> +	for (i = 0; i < mem->nr_ranges; i++) {
>> +		mstart = mem->ranges[i].start;
>> +		mend = mem->ranges[i].end;
>> +
>> +		phdr->p_type = PT_LOAD;
>> +		phdr->p_flags = PF_R|PF_W|PF_X;
>> +		phdr->p_offset  = mstart;
>> +
>> +		phdr->p_paddr = mstart;
>> +		phdr->p_vaddr = (unsigned long) __va(mstart);
>> +		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
>> +		phdr->p_align = 0;
>> +		ehdr->e_phnum++;
>> +		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
>> +			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
>> +			ehdr->e_phnum, phdr->p_offset);
>> +		phdr++;
>> +	}
>> +
>> +	*addr = buf;
>> +	*sz = elf_sz;
>> +	return 0;
>> +}
>> +
>>   Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
>>   			  void *data, size_t data_len)
>>   {
>> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
>> index 1d546dc97c50..8017eeb43036 100644
>> --- a/kernel/kexec_file.c
>> +++ b/kernel/kexec_file.c
>> @@ -1217,102 +1217,3 @@ int crash_exclude_mem_range(struct crash_mem *mem,
>>   	mem->nr_ranges++;
>>   	return 0;
>>   }
>> -
>> -int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
>> -			  void **addr, unsigned long *sz)
>> -{
>> -	Elf64_Ehdr *ehdr;
>> -	Elf64_Phdr *phdr;
>> -	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
>> -	unsigned char *buf;
>> -	unsigned int cpu, i;
>> -	unsigned long long notes_addr;
>> -	unsigned long mstart, mend;
>> -
>> -	/* extra phdr for vmcoreinfo ELF note */
>> -	nr_phdr = nr_cpus + 1;
>> -	nr_phdr += mem->nr_ranges;
>> -
>> -	/*
>> -	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
>> -	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
>> -	 * I think this is required by tools like gdb. So same physical
>> -	 * memory will be mapped in two ELF headers. One will contain kernel
>> -	 * text virtual addresses and other will have __va(physical) addresses.
>> -	 */
>> -
>> -	nr_phdr++;
>> -	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
>> -	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
>> -
>> -	buf = vzalloc(elf_sz);
>> -	if (!buf)
>> -		return -ENOMEM;
>> -
>> -	ehdr = (Elf64_Ehdr *)buf;
>> -	phdr = (Elf64_Phdr *)(ehdr + 1);
>> -	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
>> -	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
>> -	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
>> -	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
>> -	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
>> -	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
>> -	ehdr->e_type = ET_CORE;
>> -	ehdr->e_machine = ELF_ARCH;
>> -	ehdr->e_version = EV_CURRENT;
>> -	ehdr->e_phoff = sizeof(Elf64_Ehdr);
>> -	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
>> -	ehdr->e_phentsize = sizeof(Elf64_Phdr);
>> -
>> -	/* Prepare one phdr of type PT_NOTE for each present CPU */
>> -	for_each_present_cpu(cpu) {
>> -		phdr->p_type = PT_NOTE;
>> -		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
>> -		phdr->p_offset = phdr->p_paddr = notes_addr;
>> -		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
>> -		(ehdr->e_phnum)++;
>> -		phdr++;
>> -	}
>> -
>> -	/* Prepare one PT_NOTE header for vmcoreinfo */
>> -	phdr->p_type = PT_NOTE;
>> -	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
>> -	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
>> -	(ehdr->e_phnum)++;
>> -	phdr++;
>> -
>> -	/* Prepare PT_LOAD type program header for kernel text region */
>> -	if (need_kernel_map) {
>> -		phdr->p_type = PT_LOAD;
>> -		phdr->p_flags = PF_R|PF_W|PF_X;
>> -		phdr->p_vaddr = (unsigned long) _text;
>> -		phdr->p_filesz = phdr->p_memsz = _end - _text;
>> -		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
>> -		ehdr->e_phnum++;
>> -		phdr++;
>> -	}
>> -
>> -	/* Go through all the ranges in mem->ranges[] and prepare phdr */
>> -	for (i = 0; i < mem->nr_ranges; i++) {
>> -		mstart = mem->ranges[i].start;
>> -		mend = mem->ranges[i].end;
>> -
>> -		phdr->p_type = PT_LOAD;
>> -		phdr->p_flags = PF_R|PF_W|PF_X;
>> -		phdr->p_offset  = mstart;
>> -
>> -		phdr->p_paddr = mstart;
>> -		phdr->p_vaddr = (unsigned long) __va(mstart);
>> -		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
>> -		phdr->p_align = 0;
>> -		ehdr->e_phnum++;
>> -		pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
>> -			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
>> -			ehdr->e_phnum, phdr->p_offset);
>> -		phdr++;
>> -	}
>> -
>> -	*addr = buf;
>> -	*sz = elf_sz;
>> -	return 0;
>> -}
>> -- 
>> 2.31.1
>>
> 

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Re: [PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support

[Eric DeVolder]

On 8/30/22 22:26, Baoquan He wrote:
> On 08/26/22 at 01:37pm, Eric DeVolder wrote:
>> CPU and memory change notifications are received in order to
>> regenerate the elfcorehdr.
>>
>> To support cpu hotplug, a callback is registered to capture the
>> CPUHP_AP_ONLINE_DYN online and offline events via
>> cpuhp_setup_state_nocalls().
>>
>> To support memory hotplug, a notifier is registered to capture the
>> MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
>>
>> The cpu callback and memory notifiers call handle_hotplug_event()
>> which performs needed tasks and then dispatches the event to the
>> architecture specific arch_crash_handle_hotplug_event(). During the
>> process, the kexec_mutex is held.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   include/linux/crash_core.h |   8 +++
>>   include/linux/kexec.h      |  26 +++++++
>>   kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 168 insertions(+)
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index de62a722431e..3b99e69b011f 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
>>   int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
>>   		unsigned long long *crash_size, unsigned long long *crash_base);
>>   
>> +#define KEXEC_CRASH_HP_REMOVE_CPU		0
>> +#define KEXEC_CRASH_HP_ADD_CPU			1
>> +#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
>                                          ~~
>                                          Nitpick, These arenot aligned,

done!

>> +#define KEXEC_CRASH_HP_ADD_MEMORY		3
>> +#define KEXEC_CRASH_HP_INVALID_CPU		-1U
>> +
>> +struct kimage;
>> +
>>   #endif /* LINUX_CRASH_CORE_H */
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 4eefa631e0ae..9597b41136ec 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -374,6 +374,13 @@ struct kimage {
>>   	struct purgatory_info purgatory_info;
>>   #endif
>>   
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +	bool hotplug_event;
>> +	unsigned int offlinecpu;
>> +	bool elfcorehdr_index_valid;
>> +	int elfcorehdr_index;
>> +#endif
>> +
>>   #ifdef CONFIG_IMA_KEXEC
>>   	/* Virtual address of IMA measurement buffer for kexec syscall */
>>   	void *ima_buffer;
>> @@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
>>   static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
>>   #endif
>>   
>> +#ifndef arch_map_crash_pages
>> +static inline void *arch_map_crash_pages(unsigned long paddr,
>> +		unsigned long size)
>> +{
>> +	return NULL;
>> +}
>> +#endif
>> +
>> +#ifndef arch_unmap_crash_pages
>> +static inline void arch_unmap_crash_pages(void **ptr) { }
>> +#endif
>> +
>> +#ifndef arch_crash_handle_hotplug_event
>> +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
>> +		unsigned int hp_action)
>> +{
>> +}
>> +#endif
>> +
>>   #else /* !CONFIG_KEXEC_CORE */
>>   struct pt_regs;
>>   struct task_struct;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 0f8aa659cca4..455150205ded 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -11,6 +11,8 @@
>>   #include <linux/vmalloc.h>
>>   #include <linux/sizes.h>
>>   #include <linux/kexec.h>
>> +#include <linux/memory.h>
>> +#include <linux/cpuhotplug.h>
>>   
>>   #include <asm/page.h>
>>   #include <asm/sections.h>
>> @@ -18,6 +20,7 @@
>>   #include <crypto/sha1.h>
>>   
>>   #include "kallsyms_internal.h"
>> +#include "kexec_internal.h"
>>   
>>   /* vmcoreinfo stuff */
>>   unsigned char *vmcoreinfo_data;
>> @@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
>>   }
>>   
>>   subsys_initcall(crash_save_vmcoreinfo_init);
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +/*
>> + * 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.
>> + *
>> + * In order to make changes to elfcorehdr, two conditions are needed:
>> + * First, the segment containing the elfcorehdr must be large enough
>> + * to permit a growing number of resources. The elfcorehdr memory is
>> + * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
>> + * 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).
>> + */
>> +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
>> +{
>> +	/* Obtain lock while changing crash information */
>> +	mutex_lock(&kexec_mutex);
>> +
>> +	/* Check kdump is loaded */
>> +	if (kexec_crash_image) {
>> +		struct kimage *image = kexec_crash_image;
>> +
>> +		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
>> +			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
>> +			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
>> +		else
>> +			pr_debug("crash hp: hp_action %u", hp_action);
>                                                         ^~ "\n" missed
done!

>> +		/*
>> +		 * When the struct kimage is alloced, it is wiped to zero, so
>                                               ~~~~ alloced is confusing, s/alloced/allocated/
>                                              We can accept alloc being used, alloced is a little weird.

done!

>> +		 * the elfcorehdr_index_valid defaults to false. Find the
>> +		 * segment containing the elfcorehdr, if not already found.
>> +		 * This works for both the kexec_load and kexec_file_load paths.
>> +		 */
>> +		if (!image->elfcorehdr_index_valid) {
>> +			unsigned char *ptr;
>> +			unsigned long mem, memsz;
>> +			unsigned int n;
>> +
>> +			for (n = 0; n < image->nr_segments; n++) {
>> +				mem = image->segment[n].mem;
>> +				memsz = image->segment[n].memsz;
>> +				ptr = arch_map_crash_pages(mem, memsz);
> OK, I see. You want to avoid the over 80 chars line, so introducing
> two local variables. We may be able to tolerate that in this case. No
> strong opinion, let's see if other people have concern about it.
> 
> Other than these nitpicks, this patch looks good to me.
> Acked-by: Baoquan He <bhe@redhat.com>

Thank you!
eric

> 
>> +				if (ptr) {
>> +					/* The segment containing elfcorehdr */
>> +					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
>> +						image->elfcorehdr_index = (int)n;
>> +						image->elfcorehdr_index_valid = true;
>> +					}
>> +				}
>> +				arch_unmap_crash_pages((void **)&ptr);
>> +			}
>> +		}
>> +
>> +		if (!image->elfcorehdr_index_valid) {
>> +			pr_err("crash hp: unable to locate elfcorehdr segment");
>> +			goto out;
>> +		}
>> +
>> +		/* Needed in order for the segments to be updated */
>> +		arch_kexec_unprotect_crashkres();
>> +
>> +		/* Flag to differentiate between normal load and hotplug */
>> +		image->hotplug_event = true;
>> +
>> +		/* Now invoke arch-specific update handler */
>> +		arch_crash_handle_hotplug_event(image, hp_action);
>> +
>> +		/* No longer handling a hotplug event */
>> +		image->hotplug_event = false;
>> +
>> +		/* Change back to read-only */
>> +		arch_kexec_protect_crashkres();
>> +	}
>> +
>> +out:
>> +	/* Release lock now that update complete */
>> +	mutex_unlock(&kexec_mutex);
>> +}
>> +
>> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
>> +{
>> +	switch (val) {
>> +	case MEM_ONLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
>> +		break;
>> +
>> +	case MEM_OFFLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
>> +		break;
>> +	}
>> +	return NOTIFY_OK;
>> +}
>> +
>> +static struct notifier_block crash_memhp_nb = {
>> +	.notifier_call = crash_memhp_notifier,
>> +	.priority = 0
>> +};
>> +
>> +static int crash_cpuhp_online(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int crash_cpuhp_offline(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int __init crash_hotplug_init(void)
>> +{
>> +	int result = 0;
>> +
>> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> +		register_memory_notifier(&crash_memhp_nb);
>> +
>> +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
>> +		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> +						   "crash/cpuhp",
>> +						   crash_cpuhp_online,
>> +						   crash_cpuhp_offline);
>> +
>> +	return result;
>> +}
>> +
>> +subsys_initcall(crash_hotplug_init);
>> +#endif
>> -- 
>> 2.31.1
>>
> 

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Re: [PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support

[Eric DeVolder]

On 8/30/22 22:26, Baoquan He wrote:
> On 08/26/22 at 01:37pm, Eric DeVolder wrote:
>> CPU and memory change notifications are received in order to
>> regenerate the elfcorehdr.
>>
>> To support cpu hotplug, a callback is registered to capture the
>> CPUHP_AP_ONLINE_DYN online and offline events via
>> cpuhp_setup_state_nocalls().
>>
>> To support memory hotplug, a notifier is registered to capture the
>> MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
>>
>> The cpu callback and memory notifiers call handle_hotplug_event()
>> which performs needed tasks and then dispatches the event to the
>> architecture specific arch_crash_handle_hotplug_event(). During the
>> process, the kexec_mutex is held.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   include/linux/crash_core.h |   8 +++
>>   include/linux/kexec.h      |  26 +++++++
>>   kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 168 insertions(+)
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index de62a722431e..3b99e69b011f 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
>>   int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
>>   		unsigned long long *crash_size, unsigned long long *crash_base);
>>   
>> +#define KEXEC_CRASH_HP_REMOVE_CPU		0
>> +#define KEXEC_CRASH_HP_ADD_CPU			1
>> +#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
>                                          ~~
>                                          Nitpick, These arenot aligned,

done!

>> +#define KEXEC_CRASH_HP_ADD_MEMORY		3
>> +#define KEXEC_CRASH_HP_INVALID_CPU		-1U
>> +
>> +struct kimage;
>> +
>>   #endif /* LINUX_CRASH_CORE_H */
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 4eefa631e0ae..9597b41136ec 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -374,6 +374,13 @@ struct kimage {
>>   	struct purgatory_info purgatory_info;
>>   #endif
>>   
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +	bool hotplug_event;
>> +	unsigned int offlinecpu;
>> +	bool elfcorehdr_index_valid;
>> +	int elfcorehdr_index;
>> +#endif
>> +
>>   #ifdef CONFIG_IMA_KEXEC
>>   	/* Virtual address of IMA measurement buffer for kexec syscall */
>>   	void *ima_buffer;
>> @@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
>>   static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
>>   #endif
>>   
>> +#ifndef arch_map_crash_pages
>> +static inline void *arch_map_crash_pages(unsigned long paddr,
>> +		unsigned long size)
>> +{
>> +	return NULL;
>> +}
>> +#endif
>> +
>> +#ifndef arch_unmap_crash_pages
>> +static inline void arch_unmap_crash_pages(void **ptr) { }
>> +#endif
>> +
>> +#ifndef arch_crash_handle_hotplug_event
>> +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
>> +		unsigned int hp_action)
>> +{
>> +}
>> +#endif
>> +
>>   #else /* !CONFIG_KEXEC_CORE */
>>   struct pt_regs;
>>   struct task_struct;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 0f8aa659cca4..455150205ded 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -11,6 +11,8 @@
>>   #include <linux/vmalloc.h>
>>   #include <linux/sizes.h>
>>   #include <linux/kexec.h>
>> +#include <linux/memory.h>
>> +#include <linux/cpuhotplug.h>
>>   
>>   #include <asm/page.h>
>>   #include <asm/sections.h>
>> @@ -18,6 +20,7 @@
>>   #include <crypto/sha1.h>
>>   
>>   #include "kallsyms_internal.h"
>> +#include "kexec_internal.h"
>>   
>>   /* vmcoreinfo stuff */
>>   unsigned char *vmcoreinfo_data;
>> @@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
>>   }
>>   
>>   subsys_initcall(crash_save_vmcoreinfo_init);
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +/*
>> + * 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.
>> + *
>> + * In order to make changes to elfcorehdr, two conditions are needed:
>> + * First, the segment containing the elfcorehdr must be large enough
>> + * to permit a growing number of resources. The elfcorehdr memory is
>> + * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
>> + * 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).
>> + */
>> +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
>> +{
>> +	/* Obtain lock while changing crash information */
>> +	mutex_lock(&kexec_mutex);
>> +
>> +	/* Check kdump is loaded */
>> +	if (kexec_crash_image) {
>> +		struct kimage *image = kexec_crash_image;
>> +
>> +		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
>> +			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
>> +			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
>> +		else
>> +			pr_debug("crash hp: hp_action %u", hp_action);
>                                                         ^~ "\n" missed
done!

>> +		/*
>> +		 * When the struct kimage is alloced, it is wiped to zero, so
>                                               ~~~~ alloced is confusing, s/alloced/allocated/
>                                              We can accept alloc being used, alloced is a little weird.

done!

>> +		 * the elfcorehdr_index_valid defaults to false. Find the
>> +		 * segment containing the elfcorehdr, if not already found.
>> +		 * This works for both the kexec_load and kexec_file_load paths.
>> +		 */
>> +		if (!image->elfcorehdr_index_valid) {
>> +			unsigned char *ptr;
>> +			unsigned long mem, memsz;
>> +			unsigned int n;
>> +
>> +			for (n = 0; n < image->nr_segments; n++) {
>> +				mem = image->segment[n].mem;
>> +				memsz = image->segment[n].memsz;
>> +				ptr = arch_map_crash_pages(mem, memsz);
> OK, I see. You want to avoid the over 80 chars line, so introducing
> two local variables. We may be able to tolerate that in this case. No
> strong opinion, let's see if other people have concern about it.
> 
> Other than these nitpicks, this patch looks good to me.
> Acked-by: Baoquan He <bhe@redhat.com>

Thank you!
eric

> 
>> +				if (ptr) {
>> +					/* The segment containing elfcorehdr */
>> +					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
>> +						image->elfcorehdr_index = (int)n;
>> +						image->elfcorehdr_index_valid = true;
>> +					}
>> +				}
>> +				arch_unmap_crash_pages((void **)&ptr);
>> +			}
>> +		}
>> +
>> +		if (!image->elfcorehdr_index_valid) {
>> +			pr_err("crash hp: unable to locate elfcorehdr segment");
>> +			goto out;
>> +		}
>> +
>> +		/* Needed in order for the segments to be updated */
>> +		arch_kexec_unprotect_crashkres();
>> +
>> +		/* Flag to differentiate between normal load and hotplug */
>> +		image->hotplug_event = true;
>> +
>> +		/* Now invoke arch-specific update handler */
>> +		arch_crash_handle_hotplug_event(image, hp_action);
>> +
>> +		/* No longer handling a hotplug event */
>> +		image->hotplug_event = false;
>> +
>> +		/* Change back to read-only */
>> +		arch_kexec_protect_crashkres();
>> +	}
>> +
>> +out:
>> +	/* Release lock now that update complete */
>> +	mutex_unlock(&kexec_mutex);
>> +}
>> +
>> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
>> +{
>> +	switch (val) {
>> +	case MEM_ONLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
>> +		break;
>> +
>> +	case MEM_OFFLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
>> +		break;
>> +	}
>> +	return NOTIFY_OK;
>> +}
>> +
>> +static struct notifier_block crash_memhp_nb = {
>> +	.notifier_call = crash_memhp_notifier,
>> +	.priority = 0
>> +};
>> +
>> +static int crash_cpuhp_online(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int crash_cpuhp_offline(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int __init crash_hotplug_init(void)
>> +{
>> +	int result = 0;
>> +
>> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> +		register_memory_notifier(&crash_memhp_nb);
>> +
>> +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
>> +		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> +						   "crash/cpuhp",
>> +						   crash_cpuhp_online,
>> +						   crash_cpuhp_offline);
>> +
>> +	return result;
>> +}
>> +
>> +subsys_initcall(crash_hotplug_init);
>> +#endif
>> -- 
>> 2.31.1
>>
> 

Re: [PATCH v11 7/7] x86/crash: Add x86 crash hotplug support

[Baoquan He]

On 08/26/22 at 01:37pm, 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.
> 
> When loading the crash kernel via kexec_load or kexec_file_load,
> the elfcorehdr is identified at run time in
> crash_core:handle_hotplug_event().
> 
> 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. The kexec_load is also supported, but also
> requires a corresponding change to userspace kexec-tools.
> 
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> ---
>  arch/x86/Kconfig             |  11 ++++
>  arch/x86/include/asm/kexec.h |  20 +++++++
>  arch/x86/kernel/crash.c      | 102 +++++++++++++++++++++++++++++++++++
>  3 files changed, 133 insertions(+)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f9920f1341c8..cdfc9b2fdf98 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2056,6 +2056,17 @@ 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/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
> index a3760ca796aa..432073385b2d 100644
> --- a/arch/x86/include/asm/kexec.h
> +++ b/arch/x86/include/asm/kexec.h
> @@ -212,6 +212,26 @@ typedef void crash_vmclear_fn(void);
>  extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
>  extern void kdump_nmi_shootdown_cpus(void);
>  
> +void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
> +#define arch_map_crash_pages arch_map_crash_pages
> +
> +void arch_unmap_crash_pages(void **ptr);
> +#define arch_unmap_crash_pages arch_unmap_crash_pages
> +
> +void arch_crash_handle_hotplug_event(struct kimage *image,
> +		unsigned int hp_action);
> +#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
> +
> +#ifdef CONFIG_HOTPLUG_CPU
> +static inline int crash_hotplug_cpu_support(void) { return 1; }
> +#define crash_hotplug_cpu_support crash_hotplug_cpu_support
> +#endif
> +
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +static inline int crash_hotplug_memory_support(void) { return 1; }
> +#define crash_hotplug_memory_support crash_hotplug_memory_support
> +#endif

Check these two functions again, wonder whether this is a common usage
to show support of a feature. I don't remember where we do like this. We
usually define a global variable to mark it? Anyway, it works. See if
other people have comments, I could be ignorant.

Other than this tiny concern, this patch looks good to me:

Acked-by: Baoquan He <bhe@redhat.com>

> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_X86_KEXEC_H */
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 9ceb93c176a6..8fc7d678ac72 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>
> @@ -397,7 +398,18 @@ 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);
> +	/* Mark as usable to crash kernel, else crash kernel fails on boot */
> +	image->elf_headers_sz = kbuf.memsz;
> +	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);
> @@ -412,3 +424,93 @@ int crash_load_segments(struct kimage *image)
>  	return ret;
>  }
>  #endif /* CONFIG_KEXEC_FILE */
> +
> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> +/*
> + * 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 *arch_map_crash_pages(unsigned long paddr, unsigned long size)
> +{
> +	void *ptr = NULL;
> +
> +	if (size > 0) {
> +		struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
> +
> +		ptr = kmap_local_page(page);
> +	}
> +
> +	return ptr;
> +}
> +
> +void arch_unmap_crash_pages(void **ptr)
> +{
> +	if (ptr) {
> +		if (*ptr)
> +			kunmap_local(*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
> + *
> + * To accurately reflect hot un/plug changes, the new elfcorehdr
> + * is prepared in a kernel buffer, and then it is written on top
> + * of the existing/old elfcorehdr.
> + */
> +void arch_crash_handle_hotplug_event(struct kimage *image,
> +	unsigned int hp_action)
> +{
> +	struct kexec_segment *ksegment;
> +	unsigned char *ptr = NULL;
> +	unsigned long elfsz = 0;
> +	void *elfbuf = NULL;
> +	unsigned long mem, memsz;
> +
> +	/*
> +	 * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event()
> +	 */
> +	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;
> +	}
> +	if (elfsz > memsz) {
> +		pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu",
> +			elfsz, memsz);
> +		goto out;
> +	}
> +
> +	/*
> +	 * At this point, we are all but assured of success.
> +	 * Copy new elfcorehdr into destination.
> +	 */
> +	ptr = arch_map_crash_pages(mem, memsz);
> +	if (ptr) {
> +		/*
> +		 * Temporarily invalidate the crash image while the
> +		 * elfcorehdr is updated.
> +		 */
> +		xchg(&kexec_crash_image, NULL);
> +		memcpy_flushcache((void *)ptr, elfbuf, elfsz);
> +		xchg(&kexec_crash_image, image);
> +	}
> +	arch_unmap_crash_pages((void **)&ptr);
> +	pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
> +
> +out:
> +	if (elfbuf)
> +		vfree(elfbuf);
> +}
> +#endif
> -- 
> 2.31.1
> 

Re: [PATCH v11 7/7] x86/crash: Add x86 crash hotplug support

[Baoquan He]

On 08/26/22 at 01:37pm, 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.
> 
> When loading the crash kernel via kexec_load or kexec_file_load,
> the elfcorehdr is identified at run time in
> crash_core:handle_hotplug_event().
> 
> 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. The kexec_load is also supported, but also
> requires a corresponding change to userspace kexec-tools.
> 
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> ---
>  arch/x86/Kconfig             |  11 ++++
>  arch/x86/include/asm/kexec.h |  20 +++++++
>  arch/x86/kernel/crash.c      | 102 +++++++++++++++++++++++++++++++++++
>  3 files changed, 133 insertions(+)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f9920f1341c8..cdfc9b2fdf98 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2056,6 +2056,17 @@ 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/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
> index a3760ca796aa..432073385b2d 100644
> --- a/arch/x86/include/asm/kexec.h
> +++ b/arch/x86/include/asm/kexec.h
> @@ -212,6 +212,26 @@ typedef void crash_vmclear_fn(void);
>  extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
>  extern void kdump_nmi_shootdown_cpus(void);
>  
> +void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
> +#define arch_map_crash_pages arch_map_crash_pages
> +
> +void arch_unmap_crash_pages(void **ptr);
> +#define arch_unmap_crash_pages arch_unmap_crash_pages
> +
> +void arch_crash_handle_hotplug_event(struct kimage *image,
> +		unsigned int hp_action);
> +#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
> +
> +#ifdef CONFIG_HOTPLUG_CPU
> +static inline int crash_hotplug_cpu_support(void) { return 1; }
> +#define crash_hotplug_cpu_support crash_hotplug_cpu_support
> +#endif
> +
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +static inline int crash_hotplug_memory_support(void) { return 1; }
> +#define crash_hotplug_memory_support crash_hotplug_memory_support
> +#endif

Check these two functions again, wonder whether this is a common usage
to show support of a feature. I don't remember where we do like this. We
usually define a global variable to mark it? Anyway, it works. See if
other people have comments, I could be ignorant.

Other than this tiny concern, this patch looks good to me:

Acked-by: Baoquan He <bhe@redhat.com>

> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_X86_KEXEC_H */
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 9ceb93c176a6..8fc7d678ac72 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>
> @@ -397,7 +398,18 @@ 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);
> +	/* Mark as usable to crash kernel, else crash kernel fails on boot */
> +	image->elf_headers_sz = kbuf.memsz;
> +	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);
> @@ -412,3 +424,93 @@ int crash_load_segments(struct kimage *image)
>  	return ret;
>  }
>  #endif /* CONFIG_KEXEC_FILE */
> +
> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> +/*
> + * 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 *arch_map_crash_pages(unsigned long paddr, unsigned long size)
> +{
> +	void *ptr = NULL;
> +
> +	if (size > 0) {
> +		struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
> +
> +		ptr = kmap_local_page(page);
> +	}
> +
> +	return ptr;
> +}
> +
> +void arch_unmap_crash_pages(void **ptr)
> +{
> +	if (ptr) {
> +		if (*ptr)
> +			kunmap_local(*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
> + *
> + * To accurately reflect hot un/plug changes, the new elfcorehdr
> + * is prepared in a kernel buffer, and then it is written on top
> + * of the existing/old elfcorehdr.
> + */
> +void arch_crash_handle_hotplug_event(struct kimage *image,
> +	unsigned int hp_action)
> +{
> +	struct kexec_segment *ksegment;
> +	unsigned char *ptr = NULL;
> +	unsigned long elfsz = 0;
> +	void *elfbuf = NULL;
> +	unsigned long mem, memsz;
> +
> +	/*
> +	 * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event()
> +	 */
> +	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;
> +	}
> +	if (elfsz > memsz) {
> +		pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu",
> +			elfsz, memsz);
> +		goto out;
> +	}
> +
> +	/*
> +	 * At this point, we are all but assured of success.
> +	 * Copy new elfcorehdr into destination.
> +	 */
> +	ptr = arch_map_crash_pages(mem, memsz);
> +	if (ptr) {
> +		/*
> +		 * Temporarily invalidate the crash image while the
> +		 * elfcorehdr is updated.
> +		 */
> +		xchg(&kexec_crash_image, NULL);
> +		memcpy_flushcache((void *)ptr, elfbuf, elfsz);
> +		xchg(&kexec_crash_image, image);
> +	}
> +	arch_unmap_crash_pages((void **)&ptr);
> +	pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
> +
> +out:
> +	if (elfbuf)
> +		vfree(elfbuf);
> +}
> +#endif
> -- 
> 2.31.1
> 


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Re: [PATCH v11 7/7] x86/crash: Add x86 crash hotplug support

[Eric DeVolder]

On 9/4/22 22:19, Baoquan He wrote:
> On 08/26/22 at 01:37pm, 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.
>>
>> When loading the crash kernel via kexec_load or kexec_file_load,
>> the elfcorehdr is identified at run time in
>> crash_core:handle_hotplug_event().
>>
>> 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. The kexec_load is also supported, but also
>> requires a corresponding change to userspace kexec-tools.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   arch/x86/Kconfig             |  11 ++++
>>   arch/x86/include/asm/kexec.h |  20 +++++++
>>   arch/x86/kernel/crash.c      | 102 +++++++++++++++++++++++++++++++++++
>>   3 files changed, 133 insertions(+)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index f9920f1341c8..cdfc9b2fdf98 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -2056,6 +2056,17 @@ 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/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
>> index a3760ca796aa..432073385b2d 100644
>> --- a/arch/x86/include/asm/kexec.h
>> +++ b/arch/x86/include/asm/kexec.h
>> @@ -212,6 +212,26 @@ typedef void crash_vmclear_fn(void);
>>   extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
>>   extern void kdump_nmi_shootdown_cpus(void);
>>   
>> +void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
>> +#define arch_map_crash_pages arch_map_crash_pages
>> +
>> +void arch_unmap_crash_pages(void **ptr);
>> +#define arch_unmap_crash_pages arch_unmap_crash_pages
>> +
>> +void arch_crash_handle_hotplug_event(struct kimage *image,
>> +		unsigned int hp_action);
>> +#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
>> +
>> +#ifdef CONFIG_HOTPLUG_CPU
>> +static inline int crash_hotplug_cpu_support(void) { return 1; }
>> +#define crash_hotplug_cpu_support crash_hotplug_cpu_support
>> +#endif
>> +
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> +static inline int crash_hotplug_memory_support(void) { return 1; }
>> +#define crash_hotplug_memory_support crash_hotplug_memory_support
>> +#endif
> 
> Check these two functions again, wonder whether this is a common usage
> to show support of a feature. I don't remember where we do like this. We
> usually define a global variable to mark it? Anyway, it works. See if
> other people have comments, I could be ignorant.

These functions are for use in generating the value of the associated the sysfs attribute.

The default-value function (which previously was a __weak function) is in include/linux/kexec.h and 
the arch-specific override in arch/<arch>/include/asm/kexec.h. This default-value function sets the 
return to 0, for not supported.

I looked around a bit, and don't necessarily see a precedent. Then again some of this conversion of 
away from __weak is still making its way. I did briefly experiment with using a variable but decided 
there would still need to be a similar function needed (mostly likely on the subsys_initcall) in 
order to properly set the variable. So with the move away from __weak, it seemed to make sense to 
just keep the individual functions as they are now, in the spirit of the move away from __weak.

If the variable is still desired, please let me know. I'll post v12 at the end of the week to 
incorporate the fixes for some of the nits previously identified!

> 
> Other than this tiny concern, this patch looks good to me:
> 
> Acked-by: Baoquan He <bhe@redhat.com>

Thank you!
eric

> 
>> +
>>   #endif /* __ASSEMBLY__ */
>>   
>>   #endif /* _ASM_X86_KEXEC_H */
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 9ceb93c176a6..8fc7d678ac72 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>
>> @@ -397,7 +398,18 @@ 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);
>> +	/* Mark as usable to crash kernel, else crash kernel fails on boot */
>> +	image->elf_headers_sz = kbuf.memsz;
>> +	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);
>> @@ -412,3 +424,93 @@ int crash_load_segments(struct kimage *image)
>>   	return ret;
>>   }
>>   #endif /* CONFIG_KEXEC_FILE */
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +/*
>> + * 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 *arch_map_crash_pages(unsigned long paddr, unsigned long size)
>> +{
>> +	void *ptr = NULL;
>> +
>> +	if (size > 0) {
>> +		struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
>> +
>> +		ptr = kmap_local_page(page);
>> +	}
>> +
>> +	return ptr;
>> +}
>> +
>> +void arch_unmap_crash_pages(void **ptr)
>> +{
>> +	if (ptr) {
>> +		if (*ptr)
>> +			kunmap_local(*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
>> + *
>> + * To accurately reflect hot un/plug changes, the new elfcorehdr
>> + * is prepared in a kernel buffer, and then it is written on top
>> + * of the existing/old elfcorehdr.
>> + */
>> +void arch_crash_handle_hotplug_event(struct kimage *image,
>> +	unsigned int hp_action)
>> +{
>> +	struct kexec_segment *ksegment;
>> +	unsigned char *ptr = NULL;
>> +	unsigned long elfsz = 0;
>> +	void *elfbuf = NULL;
>> +	unsigned long mem, memsz;
>> +
>> +	/*
>> +	 * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event()
>> +	 */
>> +	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;
>> +	}
>> +	if (elfsz > memsz) {
>> +		pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu",
>> +			elfsz, memsz);
>> +		goto out;
>> +	}
>> +
>> +	/*
>> +	 * At this point, we are all but assured of success.
>> +	 * Copy new elfcorehdr into destination.
>> +	 */
>> +	ptr = arch_map_crash_pages(mem, memsz);
>> +	if (ptr) {
>> +		/*
>> +		 * Temporarily invalidate the crash image while the
>> +		 * elfcorehdr is updated.
>> +		 */
>> +		xchg(&kexec_crash_image, NULL);
>> +		memcpy_flushcache((void *)ptr, elfbuf, elfsz);
>> +		xchg(&kexec_crash_image, image);
>> +	}
>> +	arch_unmap_crash_pages((void **)&ptr);
>> +	pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
>> +
>> +out:
>> +	if (elfbuf)
>> +		vfree(elfbuf);
>> +}
>> +#endif
>> -- 
>> 2.31.1
>>
> 

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Re: [PATCH v11 7/7] x86/crash: Add x86 crash hotplug support

[Eric DeVolder]

On 9/4/22 22:19, Baoquan He wrote:
> On 08/26/22 at 01:37pm, 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.
>>
>> When loading the crash kernel via kexec_load or kexec_file_load,
>> the elfcorehdr is identified at run time in
>> crash_core:handle_hotplug_event().
>>
>> 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. The kexec_load is also supported, but also
>> requires a corresponding change to userspace kexec-tools.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   arch/x86/Kconfig             |  11 ++++
>>   arch/x86/include/asm/kexec.h |  20 +++++++
>>   arch/x86/kernel/crash.c      | 102 +++++++++++++++++++++++++++++++++++
>>   3 files changed, 133 insertions(+)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index f9920f1341c8..cdfc9b2fdf98 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -2056,6 +2056,17 @@ 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/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
>> index a3760ca796aa..432073385b2d 100644
>> --- a/arch/x86/include/asm/kexec.h
>> +++ b/arch/x86/include/asm/kexec.h
>> @@ -212,6 +212,26 @@ typedef void crash_vmclear_fn(void);
>>   extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
>>   extern void kdump_nmi_shootdown_cpus(void);
>>   
>> +void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
>> +#define arch_map_crash_pages arch_map_crash_pages
>> +
>> +void arch_unmap_crash_pages(void **ptr);
>> +#define arch_unmap_crash_pages arch_unmap_crash_pages
>> +
>> +void arch_crash_handle_hotplug_event(struct kimage *image,
>> +		unsigned int hp_action);
>> +#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
>> +
>> +#ifdef CONFIG_HOTPLUG_CPU
>> +static inline int crash_hotplug_cpu_support(void) { return 1; }
>> +#define crash_hotplug_cpu_support crash_hotplug_cpu_support
>> +#endif
>> +
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> +static inline int crash_hotplug_memory_support(void) { return 1; }
>> +#define crash_hotplug_memory_support crash_hotplug_memory_support
>> +#endif
> 
> Check these two functions again, wonder whether this is a common usage
> to show support of a feature. I don't remember where we do like this. We
> usually define a global variable to mark it? Anyway, it works. See if
> other people have comments, I could be ignorant.

These functions are for use in generating the value of the associated the sysfs attribute.

The default-value function (which previously was a __weak function) is in include/linux/kexec.h and 
the arch-specific override in arch/<arch>/include/asm/kexec.h. This default-value function sets the 
return to 0, for not supported.

I looked around a bit, and don't necessarily see a precedent. Then again some of this conversion of 
away from __weak is still making its way. I did briefly experiment with using a variable but decided 
there would still need to be a similar function needed (mostly likely on the subsys_initcall) in 
order to properly set the variable. So with the move away from __weak, it seemed to make sense to 
just keep the individual functions as they are now, in the spirit of the move away from __weak.

If the variable is still desired, please let me know. I'll post v12 at the end of the week to 
incorporate the fixes for some of the nits previously identified!

> 
> Other than this tiny concern, this patch looks good to me:
> 
> Acked-by: Baoquan He <bhe@redhat.com>

Thank you!
eric

> 
>> +
>>   #endif /* __ASSEMBLY__ */
>>   
>>   #endif /* _ASM_X86_KEXEC_H */
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 9ceb93c176a6..8fc7d678ac72 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>
>> @@ -397,7 +398,18 @@ 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);
>> +	/* Mark as usable to crash kernel, else crash kernel fails on boot */
>> +	image->elf_headers_sz = kbuf.memsz;
>> +	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);
>> @@ -412,3 +424,93 @@ int crash_load_segments(struct kimage *image)
>>   	return ret;
>>   }
>>   #endif /* CONFIG_KEXEC_FILE */
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +/*
>> + * 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 *arch_map_crash_pages(unsigned long paddr, unsigned long size)
>> +{
>> +	void *ptr = NULL;
>> +
>> +	if (size > 0) {
>> +		struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
>> +
>> +		ptr = kmap_local_page(page);
>> +	}
>> +
>> +	return ptr;
>> +}
>> +
>> +void arch_unmap_crash_pages(void **ptr)
>> +{
>> +	if (ptr) {
>> +		if (*ptr)
>> +			kunmap_local(*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
>> + *
>> + * To accurately reflect hot un/plug changes, the new elfcorehdr
>> + * is prepared in a kernel buffer, and then it is written on top
>> + * of the existing/old elfcorehdr.
>> + */
>> +void arch_crash_handle_hotplug_event(struct kimage *image,
>> +	unsigned int hp_action)
>> +{
>> +	struct kexec_segment *ksegment;
>> +	unsigned char *ptr = NULL;
>> +	unsigned long elfsz = 0;
>> +	void *elfbuf = NULL;
>> +	unsigned long mem, memsz;
>> +
>> +	/*
>> +	 * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event()
>> +	 */
>> +	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;
>> +	}
>> +	if (elfsz > memsz) {
>> +		pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu",
>> +			elfsz, memsz);
>> +		goto out;
>> +	}
>> +
>> +	/*
>> +	 * At this point, we are all but assured of success.
>> +	 * Copy new elfcorehdr into destination.
>> +	 */
>> +	ptr = arch_map_crash_pages(mem, memsz);
>> +	if (ptr) {
>> +		/*
>> +		 * Temporarily invalidate the crash image while the
>> +		 * elfcorehdr is updated.
>> +		 */
>> +		xchg(&kexec_crash_image, NULL);
>> +		memcpy_flushcache((void *)ptr, elfbuf, elfsz);
>> +		xchg(&kexec_crash_image, image);
>> +	}
>> +	arch_unmap_crash_pages((void **)&ptr);
>> +	pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
>> +
>> +out:
>> +	if (elfbuf)
>> +		vfree(elfbuf);
>> +}
>> +#endif
>> -- 
>> 2.31.1
>>
> 

Re: [PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support

[Eric DeVolder]

On 8/30/22 22:26, Baoquan He wrote:
> On 08/26/22 at 01:37pm, Eric DeVolder wrote:
>> CPU and memory change notifications are received in order to
>> regenerate the elfcorehdr.
>>
>> To support cpu hotplug, a callback is registered to capture the
>> CPUHP_AP_ONLINE_DYN online and offline events via
>> cpuhp_setup_state_nocalls().
>>
>> To support memory hotplug, a notifier is registered to capture the
>> MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
>>
>> The cpu callback and memory notifiers call handle_hotplug_event()
>> which performs needed tasks and then dispatches the event to the
>> architecture specific arch_crash_handle_hotplug_event(). During the
>> process, the kexec_mutex is held.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   include/linux/crash_core.h |   8 +++
>>   include/linux/kexec.h      |  26 +++++++
>>   kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 168 insertions(+)
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index de62a722431e..3b99e69b011f 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
>>   int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
>>   		unsigned long long *crash_size, unsigned long long *crash_base);
>>   
>> +#define KEXEC_CRASH_HP_REMOVE_CPU		0
>> +#define KEXEC_CRASH_HP_ADD_CPU			1
>> +#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
>                                          ~~
>                                          Nitpick, These arenot aligned,
>> +#define KEXEC_CRASH_HP_ADD_MEMORY		3
>> +#define KEXEC_CRASH_HP_INVALID_CPU		-1U
>> +
>> +struct kimage;
>> +
>>   #endif /* LINUX_CRASH_CORE_H */
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 4eefa631e0ae..9597b41136ec 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -374,6 +374,13 @@ struct kimage {
>>   	struct purgatory_info purgatory_info;
>>   #endif
>>   
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +	bool hotplug_event;
>> +	unsigned int offlinecpu;
>> +	bool elfcorehdr_index_valid;
>> +	int elfcorehdr_index;
>> +#endif
>> +
>>   #ifdef CONFIG_IMA_KEXEC
>>   	/* Virtual address of IMA measurement buffer for kexec syscall */
>>   	void *ima_buffer;
>> @@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
>>   static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
>>   #endif
>>   
>> +#ifndef arch_map_crash_pages
>> +static inline void *arch_map_crash_pages(unsigned long paddr,
>> +		unsigned long size)
>> +{
>> +	return NULL;
>> +}
>> +#endif
>> +
>> +#ifndef arch_unmap_crash_pages
>> +static inline void arch_unmap_crash_pages(void **ptr) { }
>> +#endif
>> +
>> +#ifndef arch_crash_handle_hotplug_event
>> +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
>> +		unsigned int hp_action)
>> +{
>> +}
>> +#endif
>> +
>>   #else /* !CONFIG_KEXEC_CORE */
>>   struct pt_regs;
>>   struct task_struct;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 0f8aa659cca4..455150205ded 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -11,6 +11,8 @@
>>   #include <linux/vmalloc.h>
>>   #include <linux/sizes.h>
>>   #include <linux/kexec.h>
>> +#include <linux/memory.h>
>> +#include <linux/cpuhotplug.h>
>>   
>>   #include <asm/page.h>
>>   #include <asm/sections.h>
>> @@ -18,6 +20,7 @@
>>   #include <crypto/sha1.h>
>>   
>>   #include "kallsyms_internal.h"
>> +#include "kexec_internal.h"
>>   
>>   /* vmcoreinfo stuff */
>>   unsigned char *vmcoreinfo_data;
>> @@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
>>   }
>>   
>>   subsys_initcall(crash_save_vmcoreinfo_init);
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +/*
>> + * 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.
>> + *
>> + * In order to make changes to elfcorehdr, two conditions are needed:
>> + * First, the segment containing the elfcorehdr must be large enough
>> + * to permit a growing number of resources. The elfcorehdr memory is
>> + * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
>> + * 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).
>> + */
>> +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
>> +{
>> +	/* Obtain lock while changing crash information */
>> +	mutex_lock(&kexec_mutex);
>> +
>> +	/* Check kdump is loaded */
>> +	if (kexec_crash_image) {
>> +		struct kimage *image = kexec_crash_image;
>> +
>> +		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
>> +			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
>> +			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
>> +		else
>> +			pr_debug("crash hp: hp_action %u", hp_action);
>                                                         ^~ "\n" missed
>> +		/*
>> +		 * When the struct kimage is alloced, it is wiped to zero, so
>                                               ~~~~ alloced is confusing, s/alloced/allocated/
>                                              We can accept alloc being used, alloced is a little weird.
>> +		 * the elfcorehdr_index_valid defaults to false. Find the
>> +		 * segment containing the elfcorehdr, if not already found.
>> +		 * This works for both the kexec_load and kexec_file_load paths.
>> +		 */
>> +		if (!image->elfcorehdr_index_valid) {
>> +			unsigned char *ptr;
>> +			unsigned long mem, memsz;
>> +			unsigned int n;
>> +
>> +			for (n = 0; n < image->nr_segments; n++) {
>> +				mem = image->segment[n].mem;
>> +				memsz = image->segment[n].memsz;
>> +				ptr = arch_map_crash_pages(mem, memsz);
> OK, I see. You want to avoid the over 80 chars line, so introducing
> two local variables. We may be able to tolerate that in this case. No
> strong opinion, let's see if other people have concern about it.
> 
> Other than these nitpicks, this patch looks good to me.
> Acked-by: Baoquan He <bhe@redhat.com>

Baoquan, I've had no other feedback; I've corrected the items you've pointed out in this and the 
others. I've posted v12. Note that all patches in v12 now have an Acked-by!
Thanks,
eric

> 
>> +				if (ptr) {
>> +					/* The segment containing elfcorehdr */
>> +					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
>> +						image->elfcorehdr_index = (int)n;
>> +						image->elfcorehdr_index_valid = true;
>> +					}
>> +				}
>> +				arch_unmap_crash_pages((void **)&ptr);
>> +			}
>> +		}
>> +
>> +		if (!image->elfcorehdr_index_valid) {
>> +			pr_err("crash hp: unable to locate elfcorehdr segment");
>> +			goto out;
>> +		}
>> +
>> +		/* Needed in order for the segments to be updated */
>> +		arch_kexec_unprotect_crashkres();
>> +
>> +		/* Flag to differentiate between normal load and hotplug */
>> +		image->hotplug_event = true;
>> +
>> +		/* Now invoke arch-specific update handler */
>> +		arch_crash_handle_hotplug_event(image, hp_action);
>> +
>> +		/* No longer handling a hotplug event */
>> +		image->hotplug_event = false;
>> +
>> +		/* Change back to read-only */
>> +		arch_kexec_protect_crashkres();
>> +	}
>> +
>> +out:
>> +	/* Release lock now that update complete */
>> +	mutex_unlock(&kexec_mutex);
>> +}
>> +
>> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
>> +{
>> +	switch (val) {
>> +	case MEM_ONLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
>> +		break;
>> +
>> +	case MEM_OFFLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
>> +		break;
>> +	}
>> +	return NOTIFY_OK;
>> +}
>> +
>> +static struct notifier_block crash_memhp_nb = {
>> +	.notifier_call = crash_memhp_notifier,
>> +	.priority = 0
>> +};
>> +
>> +static int crash_cpuhp_online(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int crash_cpuhp_offline(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int __init crash_hotplug_init(void)
>> +{
>> +	int result = 0;
>> +
>> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> +		register_memory_notifier(&crash_memhp_nb);
>> +
>> +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
>> +		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> +						   "crash/cpuhp",
>> +						   crash_cpuhp_online,
>> +						   crash_cpuhp_offline);
>> +
>> +	return result;
>> +}
>> +
>> +subsys_initcall(crash_hotplug_init);
>> +#endif
>> -- 
>> 2.31.1
>>
> 

Re: [PATCH v11 3/7] crash: add generic infrastructure for crash hotplug support

[Eric DeVolder]

On 8/30/22 22:26, Baoquan He wrote:
> On 08/26/22 at 01:37pm, Eric DeVolder wrote:
>> CPU and memory change notifications are received in order to
>> regenerate the elfcorehdr.
>>
>> To support cpu hotplug, a callback is registered to capture the
>> CPUHP_AP_ONLINE_DYN online and offline events via
>> cpuhp_setup_state_nocalls().
>>
>> To support memory hotplug, a notifier is registered to capture the
>> MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
>>
>> The cpu callback and memory notifiers call handle_hotplug_event()
>> which performs needed tasks and then dispatches the event to the
>> architecture specific arch_crash_handle_hotplug_event(). During the
>> process, the kexec_mutex is held.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   include/linux/crash_core.h |   8 +++
>>   include/linux/kexec.h      |  26 +++++++
>>   kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 168 insertions(+)
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index de62a722431e..3b99e69b011f 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
>>   int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
>>   		unsigned long long *crash_size, unsigned long long *crash_base);
>>   
>> +#define KEXEC_CRASH_HP_REMOVE_CPU		0
>> +#define KEXEC_CRASH_HP_ADD_CPU			1
>> +#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
>                                          ~~
>                                          Nitpick, These arenot aligned,
>> +#define KEXEC_CRASH_HP_ADD_MEMORY		3
>> +#define KEXEC_CRASH_HP_INVALID_CPU		-1U
>> +
>> +struct kimage;
>> +
>>   #endif /* LINUX_CRASH_CORE_H */
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 4eefa631e0ae..9597b41136ec 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -374,6 +374,13 @@ struct kimage {
>>   	struct purgatory_info purgatory_info;
>>   #endif
>>   
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +	bool hotplug_event;
>> +	unsigned int offlinecpu;
>> +	bool elfcorehdr_index_valid;
>> +	int elfcorehdr_index;
>> +#endif
>> +
>>   #ifdef CONFIG_IMA_KEXEC
>>   	/* Virtual address of IMA measurement buffer for kexec syscall */
>>   	void *ima_buffer;
>> @@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
>>   static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
>>   #endif
>>   
>> +#ifndef arch_map_crash_pages
>> +static inline void *arch_map_crash_pages(unsigned long paddr,
>> +		unsigned long size)
>> +{
>> +	return NULL;
>> +}
>> +#endif
>> +
>> +#ifndef arch_unmap_crash_pages
>> +static inline void arch_unmap_crash_pages(void **ptr) { }
>> +#endif
>> +
>> +#ifndef arch_crash_handle_hotplug_event
>> +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
>> +		unsigned int hp_action)
>> +{
>> +}
>> +#endif
>> +
>>   #else /* !CONFIG_KEXEC_CORE */
>>   struct pt_regs;
>>   struct task_struct;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 0f8aa659cca4..455150205ded 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -11,6 +11,8 @@
>>   #include <linux/vmalloc.h>
>>   #include <linux/sizes.h>
>>   #include <linux/kexec.h>
>> +#include <linux/memory.h>
>> +#include <linux/cpuhotplug.h>
>>   
>>   #include <asm/page.h>
>>   #include <asm/sections.h>
>> @@ -18,6 +20,7 @@
>>   #include <crypto/sha1.h>
>>   
>>   #include "kallsyms_internal.h"
>> +#include "kexec_internal.h"
>>   
>>   /* vmcoreinfo stuff */
>>   unsigned char *vmcoreinfo_data;
>> @@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
>>   }
>>   
>>   subsys_initcall(crash_save_vmcoreinfo_init);
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +/*
>> + * 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.
>> + *
>> + * In order to make changes to elfcorehdr, two conditions are needed:
>> + * First, the segment containing the elfcorehdr must be large enough
>> + * to permit a growing number of resources. The elfcorehdr memory is
>> + * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
>> + * 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).
>> + */
>> +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
>> +{
>> +	/* Obtain lock while changing crash information */
>> +	mutex_lock(&kexec_mutex);
>> +
>> +	/* Check kdump is loaded */
>> +	if (kexec_crash_image) {
>> +		struct kimage *image = kexec_crash_image;
>> +
>> +		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
>> +			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
>> +			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
>> +		else
>> +			pr_debug("crash hp: hp_action %u", hp_action);
>                                                         ^~ "\n" missed
>> +		/*
>> +		 * When the struct kimage is alloced, it is wiped to zero, so
>                                               ~~~~ alloced is confusing, s/alloced/allocated/
>                                              We can accept alloc being used, alloced is a little weird.
>> +		 * the elfcorehdr_index_valid defaults to false. Find the
>> +		 * segment containing the elfcorehdr, if not already found.
>> +		 * This works for both the kexec_load and kexec_file_load paths.
>> +		 */
>> +		if (!image->elfcorehdr_index_valid) {
>> +			unsigned char *ptr;
>> +			unsigned long mem, memsz;
>> +			unsigned int n;
>> +
>> +			for (n = 0; n < image->nr_segments; n++) {
>> +				mem = image->segment[n].mem;
>> +				memsz = image->segment[n].memsz;
>> +				ptr = arch_map_crash_pages(mem, memsz);
> OK, I see. You want to avoid the over 80 chars line, so introducing
> two local variables. We may be able to tolerate that in this case. No
> strong opinion, let's see if other people have concern about it.
> 
> Other than these nitpicks, this patch looks good to me.
> Acked-by: Baoquan He <bhe@redhat.com>

Baoquan, I've had no other feedback; I've corrected the items you've pointed out in this and the 
others. I've posted v12. Note that all patches in v12 now have an Acked-by!
Thanks,
eric

> 
>> +				if (ptr) {
>> +					/* The segment containing elfcorehdr */
>> +					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
>> +						image->elfcorehdr_index = (int)n;
>> +						image->elfcorehdr_index_valid = true;
>> +					}
>> +				}
>> +				arch_unmap_crash_pages((void **)&ptr);
>> +			}
>> +		}
>> +
>> +		if (!image->elfcorehdr_index_valid) {
>> +			pr_err("crash hp: unable to locate elfcorehdr segment");
>> +			goto out;
>> +		}
>> +
>> +		/* Needed in order for the segments to be updated */
>> +		arch_kexec_unprotect_crashkres();
>> +
>> +		/* Flag to differentiate between normal load and hotplug */
>> +		image->hotplug_event = true;
>> +
>> +		/* Now invoke arch-specific update handler */
>> +		arch_crash_handle_hotplug_event(image, hp_action);
>> +
>> +		/* No longer handling a hotplug event */
>> +		image->hotplug_event = false;
>> +
>> +		/* Change back to read-only */
>> +		arch_kexec_protect_crashkres();
>> +	}
>> +
>> +out:
>> +	/* Release lock now that update complete */
>> +	mutex_unlock(&kexec_mutex);
>> +}
>> +
>> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
>> +{
>> +	switch (val) {
>> +	case MEM_ONLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
>> +		break;
>> +
>> +	case MEM_OFFLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
>> +		break;
>> +	}
>> +	return NOTIFY_OK;
>> +}
>> +
>> +static struct notifier_block crash_memhp_nb = {
>> +	.notifier_call = crash_memhp_notifier,
>> +	.priority = 0
>> +};
>> +
>> +static int crash_cpuhp_online(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int crash_cpuhp_offline(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int __init crash_hotplug_init(void)
>> +{
>> +	int result = 0;
>> +
>> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> +		register_memory_notifier(&crash_memhp_nb);
>> +
>> +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
>> +		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> +						   "crash/cpuhp",
>> +						   crash_cpuhp_online,
>> +						   crash_cpuhp_offline);
>> +
>> +	return result;
>> +}
>> +
>> +subsys_initcall(crash_hotplug_init);
>> +#endif
>> -- 
>> 2.31.1
>>
> 

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