Re: [PATCH v3 6/8] target/i386/intel-pt: Enable host pass through of Intel PT

[Chenyi Qiang]

On 12/8/2022 2:25 PM, Xiaoyao Li wrote:
> commit e37a5c7fa459 ("i386: Add Intel Processor Trace feature support")
> added the support of Intel PT by making CPUID[14] of PT as fixed feature
> set (from ICX) for any CPU model on any host. This truly breaks the PT
> exposure on Intel SPR platform because SPR has less supported bitmap of
> CPUID(0x14,1):EBX[15:0] than ICX.
> 
> To fix the problem, enable pass through of host's PT capabilities for
> the cases "-cpu host/max" that it won't use default fixed PT feature set
> of ICX but expand automatically based on get_supported_cpuid reported by
> host. Meanwhile, it needs to ensure named CPU model still has the fixed
> PT feature set to not break the live migration case of
> "-cpu named_cpu_model,+intel-pt"
> 
> Introduces env->use_default_intel_pt flag.
>  - True means it's old CPU model that uses fixed PT feature set of ICX.
>  - False means the named CPU model has its own PT feature set.
> 
> Besides, to keep the same behavior for old CPU models that validate PT
> feature set against default fixed PT feature set of ICX in addition to
> validate from host's capabilities (via get_supported_cpuid) in
> x86_cpu_filter_features().
> 
> In the future, new named CPU model, e.g., Sapphire Rapids, can define
> its own PT feature set by setting @has_specific_intel_pt_feature_set to


It seems @has_specific_intel_pt_feature_set is not introduced in this
series. Then don't need to mention the specific flag name here.

> true and defines it's own FEAT_14_0_EBX, FEAT_14_0_ECX, FEAT_14_1_EAX
> and FEAT_14_1_EBX.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---