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Date:   Tue, 5 Jul 2022 10:17:44 -0500
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Subject: Re: [PATCH v9 0/7] crash: Kernel handling of CPU and memory hot
 un/plug
Content-Language: en-US
To:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com,
        nramas@linux.microsoft.com, thomas.lendacky@amd.com,
        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        sourabhjain@linux.ibm.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com
References: <20220613224240.79400-1-eric.devolder@oracle.com>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <20220613224240.79400-1-eric.devolder@oracle.com>
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Nudge...
Thanks!
eric


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