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

Elliott, Robert (Servers)
2022-11-02T14:29:06Z

> 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