Re: [PATCH 17/37] x86, pkeys: add functions to fetch PKRU

From	Dave Hansen <dave@sr71.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH 17/37] x86, pkeys: add functions to fetch PKRU
Date	2015-11-30 17:00 +0100
Message-ID	<qAz1U-5xV-17@gated-at.bofh.it> (permalink)
References	<qvFhE-7YL-5@gated-at.bofh.it> <qvFrj-82I-5@gated-at.bofh.it> <qznYR-18E-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 11/27/2015 01:51 AM, Thomas Gleixner wrote:
> On Mon, 16 Nov 2015, Dave Hansen wrote:
>> +#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
>> +static inline u32 __read_pkru(void)
>> +{
>> +	unsigned int eax, edx;
>> +	unsigned int ecx = 0;
>> +	unsigned int pkru;
>> +
>> +	asm volatile(".byte 0x0f,0x01,0xee\n\t"
>> +		     : "=a" (eax), "=d" (edx)
>> +		     : "c" (ecx));
>> +	pkru = eax;
>> +	return pkru;
> 
> Wouldn't a simple 'return eax;' be sufficient?

Yes.  I wanted to make it clear that EAX specifically was where the data
we want was ending up.  But, I guess the "=a" does that equally well.

I'll fix it up.

Also, looking at this, it also deserves a mention that this is the
"rdpkru" instruction.  Otherwise, it's hard to figure out what
instruction this is.

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[PATCH 17/37] x86, pkeys: add functions to fetch PKRU Dave Hansen <dave@sr71.net> - 2015-11-17 04:50 +0100
  Re: [PATCH 17/37] x86, pkeys: add functions to fetch PKRU Thomas Gleixner <tglx@linutronix.de> - 2015-11-27 11:00 +0100
    Re: [PATCH 17/37] x86, pkeys: add functions to fetch PKRU Dave Hansen <dave@sr71.net> - 2015-11-30 17:00 +0100

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