Re: [PATCH] x86/bus_lock: Don't assume the init value of DEBUGCTLMSR.BUS_LOCK_DETECT to be zero

[Sean Christopherson]

On Wed, Sep 01, 2021, Chenyi Qiang 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.

This feels like the kernel should explicitly zero out the entire MSR somewhere
in the generic boot flow.  E.g. something like this somewhere.

#ifndef CONFIG_X86_DEBUGCTLMSR
	if (boot_cpu_data.x86 < 6)
		return;
#endifa

	wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);