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

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Message-ID: <YukBz6t1n3aMbznT@gmail.com>
Date:   Tue, 2 Aug 2022 12:51:59 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Chenyi Qiang <chenyi.qiang@...el.com>
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


* 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?)

Thanks,

	Ingo