Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support

[Eric DeVolder]

On 9/30/22 12:40, Borislav Petkov wrote:
> On Fri, Sep 30, 2022 at 12:11:26PM -0500, Eric DeVolder wrote:
> > There is of course a way to enumerate the memory regions in use on the
> > machine, that is not what this code needs. In order to compute the maximum
> > buffer size needed (this buffer size is computed once), the count of the
> > maximum number of memory regions possible (even if not currently in use) is
> > what is needed.
>
> Isn't that max number documented somewhere in memory hotplug docs?
>
> Because then you don't need that Kconfig item either. Imagine you're a
> distro kernel distributor and you want crash to work on all machines
> your kernel works.
>
> So you go and set that number to max. And that would be the 99% of the
> kernel configs out there.
>
> Which means, you can just set it to max without a Kconfig item.
>
> > Oh, that would be an error of haste on my part. This should be:
> >    depends on CRASH_DUMP && MEMORY_HOTPLUG
>
> You need a Kconfig item which enables all this gunk as MEMORY_HOTPLUG is
> not a omnipresent feature. And that Kconfig item should depend on the
> other Kconfig items of the technology you need.

I once had CONFIG_CRASH_HOTPLUG, but you disagreed.

https://lore.kernel.org/lkml/Ylgot+LUDQl+G%2F5N@xxxxxxx/

From there I simply went with

 #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)

which route do you prefer?

Thanks!
eric

> > Baoquan pointed me to:
> >
> > https://lore.kernel.org/lkml/cover.1656659357.git.naveen.n.rao@xxxxxxxxxxxxxxxxxx/T/
>
> In that thread says:
>
> "- arch_kexec_apply_relocations_add() is only overridden by x86 and s390.
>    Retain the function prototype for those and move the weak
>    implementation into the header as a static inline for other
>    architectures."
>
> So yes, that's even better.