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

H. Peter Anvin
2022-11-02T16:29:07Z

On November 2, 2022 7:27:52 AM PDT, "Elliott, Robert (Servers)" <elliott@hpe.com> wrote:
>
>> From: Paolo Bonzini <pbonzini@redhat.com>
>...
>> (2) in particular holds even on bare metal. The kernel bug here is that
>> X86_FEATURE_AVX only tells you if the instructions are _present_, not if
>> they are _usable_. Indeed, the XCR0 check is present for all other
>> files in arch/x86/crypto, either instead or in addition to
>> boot_cpu_has(X86_FEATURE_AVX).
>>
>> Maxim had sent a patch about a year ago to do it in aesni-intel-glue.c
>> but Dave told him to fix the dependencies instead
>> (https://lore.kernel.org/all/20211103124614.499580-1-
>> mlevitsk@redhat.com/).
>> What do you think of applying that patch instead?
>
>Most of the x86 crypto modules using X86_FEATURE_AVX do check
> cpu_has_xfeatures(XFEATURE_MASK_YMM, ...
>
>so it's probably prudent to add it to the rest (or remove it everywhere
>if it is not needed).
>
>1. Currently checking XSAVE YMM:
> aria_aesni_avx_glue
> blake2s-glue
> camellia_aesni_avx2_glue camellia_aesni_avx_glue
> cast5_avx_glue cast6_avx_glue
> chacha_glue
> poly1305_glue
> serpent_avx2_glue serpent_avx_glue
> sha1_ssse3_glue sha256_ssse3_glue sha512_ssse3_glue
> sm3_avx_glue
> sm4_aesni_avx2_glue sm4_aesni_avx_glue
> twofish_avx_glue
>
>Currently not checking XSAVE YMM:
> aesni-intel_glue
> curve25519-x86_64
> nhpoly1305-avx2-glue
> polyval-clmulni_glue
>
>2. Similarly, modules using X86_FEATURE_AVX512F, X86_FEATURE_AVXX512VL
>and/or X86_FEATURE_AVX512BW probably need to check XFEATURE_MASK_AVX512:
>
>Currently checking XSAVE AVX512:
> blake2s-glue
> poly1305_glue
>
>Currently not checking XSAVE AVX512:
> chacha_glue
>
>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
>
>
>

We have a dependency system for CPUID features. If you are going to do this (as opposed to "fixing" this in Qemu or just saying "don't do that, it isn't a valid hardware configuration."