linux-kernel - Re: [PATCH 05/25] x86, pkey: add PKRU xsave fields and data structure(s)

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Date:	Thu, 1 Oct 2015 10:17:19 -0700
From:	Dave Hansen <dave@...1.net>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	borntraeger@...ibm.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH 05/25] x86, pkey: add PKRU xsave fields and data
 structure(s)

On 10/01/2015 04:50 AM, Thomas Gleixner wrote:
> On Mon, 28 Sep 2015, Dave Hansen wrote:
>> +/*
>> + * State component 9: 32-bit PKRU register.
>> + */
>> +struct pkru {
>> +	u32 pkru;
>> +} __packed;
>> +
>> +struct pkru_state {
>> +	union {
>> +		struct pkru		pkru;
>> +		u8			pad_to_8_bytes[8];
>> +	};
> 
> Why do you need two structs?
> 
>     struct pkru_state {
>     	   u32 pkru;
> 	   u32 pad;
>     }
> 
> should be sufficient. So instead of
> 
>        xsave.pkru_state.pkru.pkru
> 
> you get the more obvious
> 
>        xsave.pkru_state.pkru
> 
> Hmm?

I was trying to get across that PKRU itself and the "PKRU state" are
differently-sized.

But, it does just end up looking funky if we _use_ it.  I'll fix it up.

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