From mboxrd@z Thu Jan  1 00:00:00 1970
From: Emre Can Sezer <ecsezer@ncsu.edu>
Subject: x86 instruction emulation in hvm
Date: Thu, 07 May 2009 15:39:42 -0400
Message-ID: <4A0338FE.8010400@ncsu.edu>
References: <49E50B49.7000706@ncsu.edu>
	<20090415083431.GA10010@york.uk.xensource.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <20090415083431.GA10010@york.uk.xensource.com>
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: Xen Devel <xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

I'm running an HVM guest using shadow page tables on a 64bit machine.  
I'm working on a project where I mark certain pages read-only and 
capture the writes into these pages.  I then try to emulate the write 
instructions using x86_emulate as is done in arch/x86/mm/shadow/multi.c.

The instruction I'm trying to emulate is:
asm("mov %%gs,%0" : "=m" (p->thread.gsindex));

Since the source operand is a segment register, and the x86_emulate_ops 
structure that is being used does not have a ops->read_segment function 
defined, the emulation fails.

Is there an easy way to add or activate this functionality?  Perhaps a 
full emulator, since one would expect to see other cases of memory 
writes that are not handled as well.

Thanks,

John