Re: [RFC v4 PATCH 2/5] powerpc/crash hp: introduce a new config option CRASH_HOTPLUG

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

On 4/21/22 06:34, Michael Ellerman wrote:
> Sourabh Jain <sourabhjain@linux.ibm.com> writes:
>> The option CRASH_HOTPLUG enables, in kernel update to kexec segments on
>> hotplug events.
>>
>> All the updates needed on the capture kernel load path in the kernel for
>> both kexec_load and kexec_file_load system will be kept under this config.
>>
>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
>> Reviewed-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   arch/powerpc/Kconfig | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index b779603978e1..777db33f75b5 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -623,6 +623,17 @@ config FA_DUMP
>>   	  If unsure, say "y". Only special kernels like petitboot may
>>   	  need to say "N" here.
>>   
>> +config CRASH_HOTPLUG
>> +	bool "kernel updates of crash kexec segments"
>> +	depends on CRASH_DUMP && (HOTPLUG_CPU) && KEXEC_FILE
>> +	help
>> +	  An efficient way to keep the capture kernel up-to-date with CPU
>> +	  hotplug events. On CPU hotplug event the kexec segments of capture
>> +	  kernel becomes stale and need to be updated with latest CPU data.
>> +	  In this method the kernel performs minimal update to only relevant
>> +	  kexec segments on CPU hotplug event, instead of triggering full
>> +	  capture kernel reload from userspace using udev rule.
> 
> Why would a user ever want to turn this off?
> 
> Seems to me we should just make it always behave this way, and not have
> a CONFIG option at all.

Sourabh,

Borislav Petkov also requested I remove the config option, which will be the
case in upcoming v8.

Where I was using CONFIG_CRASH_HOTPLUG, I've replaced it with the
CONFIG_HOTPLUG_CPU || CONFIG_MEMORY_HOTPLUG.

Eric

> 
> cheers
>