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

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 21/04/22 20:59, Eric DeVolder wrote:
>
>
> 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.


Yes good idea. Even Michael suggested there is no need for new CONFIG
option. I will also remove CRASH_HOTPLUG config in the next version.

Thanks,
Sourabh Jain