linux-kernel - Re: [RESEND] x86/bus_lock: Don't assume the init value of DEBUGCTLMSR.BUS_LOCK

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Message-ID: <897aa91c-9d45-e16a-9b09-849fab588cd7@intel.com>
Date:   Tue, 2 Aug 2022 19:29:30 +0800
From:   Chenyi Qiang <chenyi.qiang@...el.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [RESEND] x86/bus_lock: Don't assume the init value of
 DEBUGCTLMSR.BUS_LOCK_DETECT to be zero



On 8/2/2022 6:51 PM, Ingo Molnar wrote:
> 
> * Chenyi Qiang <chenyi.qiang@...el.com> wrote:
> 
>> It's possible that BIOS/firmware has set DEBUGCTLMSR_BUS_LOCK_DETECT, or
>> this kernel has been kexec'd from a kernel that enabled bus lock
>> detection.
>>
>> Disable bus lock detection explicitly if not wanted.
> 
> Makes sense.
> 
> Just curious: in what circumstances does the BIOS/firmware set
> DEBUGCTLMSR_BUS_LOCK_DETECT? Does it use it, or does it enable it for some
> spurious reason, without really using the feature? (Assuming you are aware
> of instances where this happened - or was this simply a hypothetical?)

Yes, It's just a hypothetical for BIOS/firmware. Kexec is the real case 
I met with this problem.

> 
> Thanks,
> 
> 	Ingo