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

[Chenyi Qiang]

On 10/20/2021 1:05 AM, Sean Christopherson wrote:
> 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.

Yes. Meanwhile, I think kernel code prefers to explicitly set/clear the 
control bit according to the parameter. Maybe both changes should be 
applied.

> #ifndef CONFIG_X86_DEBUGCTLMSR
> 	if (boot_cpu_data.x86 < 6)
> 		return;
> #endifa
>
> 	wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);