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: <Y71bW/8XZCackPLh@gmail.com>
Date:   Tue, 10 Jan 2023 13:34:35 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
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, linux-kernel@...r.kernel.org,
        x86@...nel.org, liwei391@...wei.com,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH -v2] x86/boot/compressed: Register dummy NMI handler in
 EFI boot loader, to avoid kdump crashes


* Borislav Petkov <bp@...en8.de> wrote:

> > 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.
> 
> IOW, does this help?
> 
> ---
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 7832a69d170e..55437d8a4fad 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -287,6 +287,7 @@ static noinstr void mce_panic(const char *msg, struct mce *final, char *exp)
>  		if (panic_timeout == 0)
>  			panic_timeout = mca_cfg.panic_timeout;
>  		panic(msg);
> +		mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);

So your suggestion was to exit MC context 'before' the panic() call - but 
the patch calls it 'after' - was that intentional?

Thanks,

	Ingo