linux-kernel - Re: [PATCH 2/4] x86/cpuid: refactor setup_clear_cpu_cap/clear

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Date:   Wed, 22 Jun 2022 08:07:31 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, linux-kernel@...r.kernel.org
Cc:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        Jiri Olsa <jolsa@...nel.org>, linux-perf-users@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "David S. Miller" <davem@...emloft.net>,
        Borislav Petkov <bp@...en8.de>,
        Kees Cook <keescook@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Jane Malalane <jane.malalane@...rix.com>,
        Tony Luck <tony.luck@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "open list:CRYPTO API" <linux-crypto@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 2/4] x86/cpuid: refactor setup_clear_cpu_cap/clear_feature

On 6/22/22 07:48, Maxim Levitsky wrote:
> Simplify the code a bit by always passing &boot_cpu_data
> in case the setup_clear_cpu_cap was called.
> 
> Also unify clear_cpu_cap and do_clear_cpu_cap.

Please always add a "()" suffix to functions.  "foo" is a variable, but
"foo()" is a function.

I also really like when a changelog has a clear problem statement.  I
_think_ the problem here is something along the lines of the 'c'
argument to clear_feature() having different behavior when it is NULL
versus '&boot_cpu_data'.

Basically, there's no reason to support clearing a bit in
'&boot_cpu_data' without also setting that bit in 'cpu_caps_cleared'.
>  {
> -	do_clear_cpu_cap(NULL, feature);
> +	clear_cpu_cap(&boot_cpu_data, feature);
>  }