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

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Date:   Tue, 19 Oct 2021 15:34:59 +0800
From:   Chenyi Qiang <chenyi.qiang@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/bus_lock: Don't assume the init value of
 DEBUGCTLMSR.BUS_LOCK_DETECT to be zero

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@...el.com>
>> Reviewed-by: Tony Luck <tony.luck@...el.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);
>>   }
>>