From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1756066AbbJARRb (ORCPT <rfc822;w@1wt.eu>);
	Thu, 1 Oct 2015 13:17:31 -0400
Received: from www.sr71.net ([198.145.64.142]:42247 "EHLO blackbird.sr71.net"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1754283AbbJARRa (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Thu, 1 Oct 2015 13:17:30 -0400
Subject: Re: [PATCH 05/25] x86, pkey: add PKRU xsave fields and data
 structure(s)
To: Thomas Gleixner <tglx@linutronix.de>
References: <20150928191817.035A64E2@viggo.jf.intel.com>
 <20150928191819.925D0BD3@viggo.jf.intel.com>
 <alpine.DEB.2.11.1510011303420.4500@nanos>
Cc: borntraeger@de.ibm.com, x86@kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, dave.hansen@linux.intel.com
From: Dave Hansen <dave@sr71.net>
Message-ID: <560D6A9F.2000504@sr71.net>
Date: Thu, 1 Oct 2015 10:17:19 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.2.0
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.11.1510011303420.4500@nanos>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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.