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SubjectRe: [PATCH] x86/bus_lock: Don't assume the init value of DEBUGCTLMSR.BUS_LOCK_DETECT to be zero
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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@intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
> 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);
> }
>
>

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