Re: [PATCH v2 1/5] perf/x86/intel/lbr: use setup_clear_cpu_cap instead of clear_cpu_cap

[Paolo Bonzini]

On 11/2/22 15:27, Elliott, Robert (Servers) wrote:
> 3. Similarly, modules using X86_FEATURE_XMM2 probably need to
> check XFEATURE_MASK_SSE:
>
> Currently checking XSAVE SSE:
>    aegis128-aesni-glue
>
> Current not checking XSAVE SSE:
>    nhpoly1305-sse2_glue
>    serpent_sse2_glue

These should check boot_cpu_has(X86_FEATURE_FXSR).  Checking 
XFEATURE_MASK_SSE will fail on systems without XSAVE, because 
fpu_kernel_cfg.max_features is zero there (see fpu__init_system_xstate() 
in arch/x86/kernel/fpu/xstate.c).

It happens to work for aegis128-aesni-glue because AES instructions only 
exist on new-enough parts, but it should probably be changed as well.

Paolo