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

[Chenyi Qiang]

Reminder for this minor fix.

On 9/17/2021 10:52 AM, Chenyi Qiang wrote:
> Kindly ping for this minor change.
>
> Thanks
> Chenyi
>
> On 9/1/2021 4:40 PM, 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.
> >
> > Disable bus lock detection explicitly if not wanted.
> >
> > Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
> > Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> > ---
> >   arch/x86/kernel/cpu/intel.c | 27 ++++++++++++++-------------
> >   1 file changed, 14 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> > index 8321c43554a1..38dda04d9342 100644
> > --- a/arch/x86/kernel/cpu/intel.c
> > +++ b/arch/x86/kernel/cpu/intel.c
> > @@ -1152,22 +1152,23 @@ static void bus_lock_init(void)
> >   {
> >       u64 val;
> > -    /*
> > -     * Warn and fatal are handled by #AC for split lock if #AC for
> > -     * split lock is supported.
> > -     */
> > -    if (!boot_cpu_has(X86_FEATURE_BUS_LOCK_DETECT) ||
> > -        (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) &&
> > -        (sld_state == sld_warn || sld_state == sld_fatal)) ||
> > -        sld_state == sld_off)
> > +    if (!boot_cpu_has(X86_FEATURE_BUS_LOCK_DETECT))
> >           return;
> > -    /*
> > -     * Enable #DB for bus lock. All bus locks are handled in #DB except
> > -     * split locks are handled in #AC in the fatal case.
> > -     */
> >       rdmsrl(MSR_IA32_DEBUGCTLMSR, val);
> > -    val |= DEBUGCTLMSR_BUS_LOCK_DETECT;
> > +
> > +    if ((boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) &&
> > +        (sld_state == sld_warn || sld_state == sld_fatal)) ||
> > +        sld_state == sld_off) {
> > +        /*
> > +         * Warn and fatal are handled by #AC for split lock if #AC for
> > +         * split lock is supported.
> > +         */
> > +        val &= ~DEBUGCTLMSR_BUS_LOCK_DETECT;
> > +    } else {
> > +        val |= DEBUGCTLMSR_BUS_LOCK_DETECT;
> > +    }
> > +
> >       wrmsrl(MSR_IA32_DEBUGCTLMSR, val);
> >   }