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

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Date:   Wed, 2 Nov 2022 19:49:31 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Eric DeVolder <eric.devolder@...cle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH v13 7/7] x86/crash: add x86 crash hotplug support

On Wed, Nov 02, 2022 at 11:54:08AM -0500, Eric DeVolder wrote:
> Technically the answer is no; cpu hotplug events are independent of memory
> hotplug events, but both are written into the elfcorehdr, so in reality
> yes... The elfcorehdr contains a single list of Phdrs describing CPUs and
> crash memory ranges; the entire list is re-written on a hotplug change.

Then technically also yes. Otherwise your crash information will contain
wrong CPU numbers.

How has that not been a problem until now...?

I.e., offline a bunch of CPUs and then cause a crash dump.

Hmm.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette