Re: [RFC v2 0/6] crash: Kernel handling of CPU and memory hot un/plug

[Eric DeVolder <eric.devolder@oracle.com>]

On 1/10/22 02:04, Baoquan He wrote:
> Hi Eric,
> 
> On 01/05/22 at 08:25am, Eric DeVolder wrote:
>> Nudge...
>>
>> Fwiw, below is a working changeset to kexec userspace utility that allows the kexec_load
>> path to work similarly to the kexec_file_load path of this RFC. With both the following
>> userspace kexec patch and this RFC, both kexec_load and kexec_file_load work with changes
>> due to hotplug *without* unloading-then-reloading the kdump/capture kernel.
> 
> Thanks for taking a try on that, and sorry for late response because of
> somethings at hand.
> 
> I will review this v2 round. When applying them, I encountered some
> conflict, could you please rebase these on the ltest 5.16 and send me
> a tar ball privately, or a github branch is also welcome. Thanks in
> advance.

Baoquan, thank you for your time and interest on this patch.
I posted as v3 as I incorporated changes from David Hildenbrand and some other minor tweaks.
Regards,
eric

> 
> 
> Thanks
> Baoquan
> 
>>
>> diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
>> index 9826f6d..06adb7e 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 unsigned long long hotplug_size;
>>
>>   static int get_kernel_page_offset(struct kexec_info *UNUSED(info),
>>   				  struct crash_elf_info *elf_info)
>> @@ -975,6 +976,13 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline,
>>   	} else {
>>   		memsz = bufsz;
>>   	}
>> +
>> +    /* If hotplug support enabled, use that size */
>> +    if (hotplug_size) {
>> +        memsz = hotplug_size;
>> +    }
>> +
>> +    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/kexec.c b/kexec/kexec.c
>> index f63b36b..9569d9a 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;
>> +unsigned long long hotplug_size = 0;
>>   static unsigned long kexec_flags = 0;
>>   /* Flags for kexec file (fd) based syscall */
>>   static unsigned long kexec_file_flags = 0;
>> @@ -672,6 +673,12 @@ 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 (hotplug_size && (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;
>> @@ -1504,6 +1511,17 @@ int main(int argc, char *argv[])
>>   		case OPT_PRINT_CKR_SIZE:
>>   			print_crashkernel_region_size();
>>   			return 0;
>> +		case OPT_HOTPLUG_SIZE:
>> +            /* Reserved the specified size for hotplug growth */
>> +			hotplug_size = strtoul(optarg, &endptr, 0);
>> +			if (*endptr) {
>> +				fprintf(stderr,
>> +					"Bad option value in --hotplug-size=%s\n",
>> +					optarg);
>> +				usage();
>> +				return 1;
>> +			}
>> +			break;
>>   		default:
>>   			break;
>>   		}
>> diff --git a/kexec/kexec.h b/kexec/kexec.h
>> index 595dd68..b30dda4 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_SIZE	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-size",     2, 0, OPT_HOTPLUG_SIZE }, \
>>
>>   #define KEXEC_OPT_STR "h?vdfixyluet:pscaS"
>>
>>
>>
>> On 12/7/21 13:51, 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:
>>>
>>>    - Disable the udev rule for updating kdump on hot un/plug changes
>>>      Eg. on RHEL: rm -f /usr/lib/udev/rules.d/98-kexec.rules
>>>      or other technique to neuter the rule.
>>>
>>>    - 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, on which I am current working to provide separately.
>>>
>>> Regards,
>>> eric
>>> ---
>>> RFC v2: 7dec2021
>>>    - 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 (6):
>>>     crash: fix minor typo/bug in debug message
>>>     crash hp: Introduce CRASH_HOTPLUG configuration options
>>>     crash hp: definitions and prototype changes
>>>     crash hp: generic crash hotplug support infrastructure
>>>     crash hp: kexec_file changes for crash hotplug support
>>>     crash hp: Add x86 crash hotplug support
>>>
>>>    arch/x86/Kconfig        |  26 ++++++++
>>>    arch/x86/kernel/crash.c | 140 +++++++++++++++++++++++++++++++++++++++-
>>>    include/linux/kexec.h   |  21 +++++-
>>>    kernel/crash_core.c     | 118 +++++++++++++++++++++++++++++++++
>>>    kernel/kexec_file.c     |  15 ++++-
>>>    5 files changed, 314 insertions(+), 6 deletions(-)
>>>
>>
>