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

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Date:   Wed, 22 Jun 2022 18:59:06 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Dave Hansen <dave.hansen@...el.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 Wed, 2022-06-22 at 08:07 -0700, Dave Hansen wrote:
> 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.
Will do next time!


> 
> 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'.

To be honest I didn't try to fix any problem here, I just wanted to simplify
clear_feature() a bit by avoiding a recursive call to clear_cpu_cap.

> 
> 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);
> >  }

I'll try to think about a better changelog message for this.

Thank you!
Best regards,
	Maxim Levitsky