linux-kernel - Re: [PATCH v6 03/10] x86, mpx: add macro cpu_has

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Message-ID: <53A1BD95.10701@intel.com>
Date:	Wed, 18 Jun 2014 09:25:57 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Qiaowei Ren <qiaowei.ren@...el.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 03/10] x86, mpx: add macro cpu_has_mpx

On 06/18/2014 07:59 AM, H. Peter Anvin wrote:
> On 06/18/2014 07:35 AM, Dave Hansen wrote:
>> It looks like static_cpu_has() is the right thing to use instead of
>> boot_cpu_has().  But, this doesn't just obfuscate things.
>>
>> We actually _want_ the compiler to cull code out when the config option
>> is off.  Things like do_bounds() will see code savings with _some_ kind
>> of #ifdef rather than using static_cpu_has().
>>
>> So, we can either use the well worn, consistent with other features in
>> x86, cpu_has_$foo approach.  Or, we can roll our own macros.
> 
> We could do something like:
> 
> #define MPX_ENABLED (IS_ENABLED(CONFIG_X86_MPX) &&
> static_cpu_has(X86_FEATURE_MPX))

How about something like the attached patch?

This lets us use static_cpu_has() for the checks, and allows us to
easily add new checks for other features that might be compile-time
disabled.

View attachment "x86-disabled_mask.patch" of type "text/x-patch" (3227 bytes)