Re: [PATCH v13 7/7] x86/crash: add x86 crash hotplug support

Eric DeVolder
2022-11-09T22:13:10Z

On 11/9/22 15:31, Borislav Petkov wrote:
> On Wed, Nov 09, 2022 at 09:48:33AM -0600, Eric DeVolder wrote:
>> ...
>> which then defaults HOTPLUG_CPU to on and thus this code/ifdef in question.
>
> defconfig can sometimes lag reality. In this case, the majority of
> machines have SMP=y because the majority of machines out there are,
> well, multicore.
>
>> So at this point, I'm still not sure if you want the ifdef line:
>> - removed altogether
>> - transitioned to CRASH_HOTPLUG
>> - leave as is
>
> So let's think out loud:
>
> * the majority of machines will have CONFIG_HOTPLUG_CPU=y because
> they're SMP machines and we want the elfcorehdr updates to happen when
> CPUs get offlined or onlined.
>
> CONFIG_MEMORY_HOTPLUG is most likely going to be =n on the majority of
> machines out there.
>
> (Note how the deciding factor for all this is what would make sense on
> the prevailing majority of machines out there.)
>
> And memory hotplug will be off for the simple reason that not so many
> machines have memory hotplug hardware capability.
>
> Which then means, IMHO, this functionality should be separate: have a
> CPU hotplug callback and a memory hotplug callback.
>
> And you kinda do that in
>
> Subject: [PATCH v13 3/7] crash: add generic infrastructure for crash hotplug support
>
> but then this all calls into a single handle_hotplug_event() and that
> hp_action doesn't really matter.
>
> It is used in the call to
>
> arch_crash_handle_hotplug_event(image, hp_action);
>
> but that hp_action argument is unused in the x86 version. >
> IOW, you can do this callback regardless whether it is a CPU or memory
> hotplug event.
>
> So thinking about it, a single CONFIG_CRASH_HOTPLUG which unifies those
> CPU and memory hotplug callback functionality makes most sense to me.
> Because you don't really differentiate between the two in the callback
> actions.
>
> Anyway, this is how I see it from here. I could very well be missing an
> aspect, of course.
>
> Thx.
>
OK, I'll put in CRASH_HOTPLUG! Expect v14 soon!
Thank you!
eric