Re: [PATCH 0/2] i386: Adjust CPUID_EXT_PDCM based on enable_pmu at realization

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 3/7/2025 12:22 AM, Zhao Liu wrote:
> Hi Xiaoyao,
> 
>> First, it's not a good practice that values in env->features[] cannot be
>> directly used for guest CPUID in void cpu_x86_cpuid(), but require further
>> adjustment there. env->features[] are supposed to be finalized at cpu
>> realization, so that after it env->features[] is reliable.
>>
>> Second, there is one dependency entry relates to CPUID_EXT_PDCM in
>> feature_dependencies[]. QEMU needs to get correct value of
>> CPUID_EXT_PDCM in env->features[] to ensure applying the dependencies
>> correctly.
> 
> I agree that this is a very good idea, especially since PDCM has a
> dependency entry.
> 
> "pmu" is totally a property rather than a feature bit, which makes the
> dependency relationships in the code complex. Therefore, I think it's
> worth having a series to clarify the dependencies of pmu as much as
> possible.
> 
> I remember Dapeng/Zide also have fixes for pmu dependencies, and if
> possible, I could help you combine this series with others' cleanups.

The reason I sent out this small series quickly is mainly for Dongli to 
as a reference.

In fact, there are mess on LBR enabling that it checks enable_pmu 
everytime with CPUID_7_0_EDX_ARCH_LBR as well as 
CPUID_8000_0022_EAX_PERFMON_V2. That's on my WIP list to clean it up.

I think I need to check if they are duplicated with Dapeng/Zide's series.

> Additionally, I think patch 1 and patch 2 can be merged together. Do you
> agree?

IMHO, they stand as their own. I'll leave it to Paolo to make the decision.

> Thanks,
> Zhao
>