linux-kernel - RE: [PATCH v2 1/5] perf/x86/intel/lbr: use setup_clear_cpu_cap instead of clear_cpu

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Message-ID: <MW5PR84MB18428331677C881764E615D2AB399@MW5PR84MB1842.NAMPRD84.PROD.OUTLOOK.COM>
Date:   Wed, 2 Nov 2022 14:27:52 +0000
From:   "Elliott, Robert (Servers)" <elliott@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Maxim Levitsky <mlevitsk@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        "Josh Poimboeuf" <jpoimboe@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        "Tony Luck" <tony.luck@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Arnaldo Carvalho de Melo" <acme@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Jane Malalane <jane.malalane@...rix.com>,
        "Kees Cook" <keescook@...omium.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "Jiri Olsa" <jolsa@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "open list:CRYPTO API" <linux-crypto@...r.kernel.org>
Subject: RE: [PATCH v2 1/5] perf/x86/intel/lbr: use setup_clear_cpu_cap
 instead of clear_cpu_cap


> From: Paolo Bonzini <pbonzini@...hat.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@...hat.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