Re: [PATCH 3/4] V7 more sampling fun 3

Mark,

speck for mark gross <[email protected]> writes:
> On Thu, Jan 16, 2020 at 02:16:07PM -0800, speck for mark gross wrote:
>> +	/*
>> +	 * Check to see if this is one of the MDS_NO systems supporting
>> +	 * TSX that are only exposed to SRBDS when TSX is enabled.
>> +	 */
>> +	ia32_cap = x86_read_arch_cap_msr();
>> +	if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM)) {
>> +		srbds_mitigation = SRBDS_MITIGATION_NOT_AFFECTED_TSX_OFF;
>> +		goto out;
>> +	}
>> +
>> +	if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
>> +		srbds_mitigation = SRBDS_MITIGATION_HYPERVISOR;
>> +		goto out;
>> +	}
>> +
>> +	if (!boot_cpu_has(X86_FEATURE_SRBDS_CTRL)) {
>> +		srbds_mitigation = SRBDS_MITIGATION_UCODE_NEEDED;
>> +		goto out;
>> +	}
>> +
>> +	if (cpu_mitigations_off() || srbds_off) {
>> +		if (srbds_mitigation != SRBDS_MITIGATION_NOT_AFFECTED_TSX_OFF)
>> +			srbds_mitigation = SRBDS_MITIGATION_OFF;
>> +	}
>> +out:
> The test for cpu_mitigations_off or srbds off needs to be after out:
> Otherwise when TSX is off and srbds=off will report the wrong answer.

If the CPU has SRBDS_IF_TSX and TSX is disabled then the correct
answer is: Not affected (TSX off)

That's what we do with other issues as well. If the CPU is not affected
then we print this even with mitigation disabled (all or particular).

Thanks,

        tglx