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

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Date:   Thu, 3 Nov 2022 14:30:56 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Elliott, Robert (Servers)" <elliott@....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

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