From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [Q] guest and user protection on x86-64 by paging
Date: Sun, 01 Aug 2010 23:31:59 -0700
Message-ID: <4C56665F.6030808@goop.org>
References: <4C559A4A.1030809@gatech.edu>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <4C559A4A.1030809@gatech.edu>
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Min Lee <min.lee@gatech.edu>
Cc: Xen-devel@lists.xensource.com
List-Id: xen-devel@lists.xenproject.org

  On 08/01/2010 09:01 AM, Min Lee wrote:
> Hi, folks.
> one question. I'll read source code, but if one can give me brief 
> overview, it would be so helpful. On x86-64, guest and user runs both 
> in ring 3, and protect from each other by paging mechanism. but, how? 
> Then page table should be modified and TLB would be flushed for every 
> system call. This would be some overhead, I think. Is this what Xen is 
> doing?

Yes it is.  64-bit PV guests run at a considerable disadvantage.  The 
only mitigating factor is that it sets the Global bit on usermode ptes, 
so that they don't get flushed from tlb during the transition.

     J