linux-kernel - Re: [PATCH -v2] x86/boot/compressed: Register dummy NMI handler in EFI boot loader, to avoid kdump crashes

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Date:   Tue, 10 Jan 2023 17:09:10 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Zeng Heng <zengheng4@...wei.com>
Cc:     Ingo Molnar <mingo@...nel.org>, michael.roth@....com,
        hpa@...or.com, tglx@...utronix.de,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        kirill.shutemov@...ux.intel.com, jroedel@...e.de,
        keescook@...omium.org, mingo@...hat.com,
        dave.hansen@...ux.intel.com, brijesh.singh@....com,
        linux-kernel@...r.kernel.org, x86@...nel.org, liwei391@...wei.com
Subject: Re: [PATCH -v2] x86/boot/compressed: Register dummy NMI handler in
 EFI boot loader, to avoid kdump crashes

On Tue, Jan 10, 2023 at 01:57:05PM +0100, Borislav Petkov wrote:
> I'm doubtful now as you're injecting errors so you're not really in #MC context
> but in this contrived context which is actually an NMI one. So we need to think
> about how to fix this case.

I did some more thinking:

*if* this really is a real issue - and not some silly qemu games - then
native_machine_crash_shutdown() does all the cleanup before the kdump kernel is
started.

Any NMI clearing, maybe using iret_to_self() etc, #MC resetting etc should
happen there and not anywhere else.

-- 
Regards/Gruss,
    Boris.

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