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: <0736f30a-294e-b8e0-f085-37b03e4f7efe@huawei.com>
Date:   Tue, 10 Jan 2023 20:50:10 +0800
From:   Zeng Heng <zengheng4@...wei.com>
To:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
CC:     <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


On 2023/1/10 20:34, Ingo Molnar wrote:
> * 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);

I'm willing to test any patch provided, but the panic() is never return 
and the

mce_wrmsrl() would be never called. Am I wrong?

B.R.,

Zeng Heng

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