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

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Message-ID: <Y71V8SRLxZ/Uqkfs@zn.tnic>
Date:   Tue, 10 Jan 2023 13:11:29 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Zeng Heng <zengheng4@...wei.com>, 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 01:01:06PM +0100, Ingo Molnar wrote:
> From: Zeng Heng <zengheng4@...wei.com>
> Date: Tue, 10 Jan 2023 18:27:45 +0800
> Subject: [PATCH] x86/boot/compressed: Register dummy NMI handler in EFI boot loader, to avoid kdump crashes
> 
> If kdump is enabled, when using mce_inject to inject errors, EFI

Why does "EFI" matter here? Any boot loader would do...

> boot loader would decompress & load second kernel for saving the

s/&/and/

> vmcore file.
> 
> For normal errors that is fine.

Useless sentence.

> However, in the MCE case, the panic
> CPU that firstly enters into mce_panic() is running within NMI
> interrupt context,

"#MC context" it is non-maskable but that's not "NMI interrupt context"

> and the processor blocks delivery of subsequent
> NMIs until the next execution of the IRET instruction.
> 
> When the panic CPU takes long time in the panic processing route,

I'm still unclear on the order of events here. It sounds like

1. MCE injected
2. panic
3. kdump gets loaded

If that is the case, then I presume the flow is:

mce_panic -> panic -> __crash_kexec()

Yes?

If so, then we should make sure we have *exited* #MC context before calling
panic() and not have to add hacks like this one of adding an empty NMI handler.

But I'm only speculating as it is hard to make sense of all this text.

Thx.

-- 
Regards/Gruss,
    Boris.

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