WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

[Xen-devel] RE: One potential issue of shadow fault emulation

To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>
Subject: [Xen-devel] RE: One potential issue of shadow fault emulation
From: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Date: Sat, 22 Dec 2007 00:05:08 +0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Fri, 21 Dec 2007 08:07:19 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <20071221154253.GA4805@xxxxxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <391BF3CDD2DC0848B40ACB72FA97AD5902A481F3@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20071221154253.GA4805@xxxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AchD6FOvCPmIxAuSTuC0FhRYrJlGZgAAtiCA
Thread-topic: One potential issue of shadow fault emulation
Tim Deegan <mailto:Tim.Deegan@xxxxxxxxxx> wrote:
> Hi,
> 
> At 22:58 +0800 on 21 Dec (1198277929), Jiang, Yunhong wrote:
>> Currently shadow fault handler try to emulate up to four extra
>> instruction for PAE guest, to reduce vmexit times.
>> 
>> But there is a potential issue here: Consider the second instruction
is
>> a change to virtual TPR register. In physical environment, if the TPR
>> acceleration is enabled, the cpu will try to access the
>> VIRTUAL_APIC_PAGE_ADDR set in the VMCS. However, when we do
emulation,
>> we didn't cope with this situation, and will access the
APIC_ACCESS_ADDR
>> page pointed by the shadow. This is sure cause problem to guest,
usually
>> blue screen, and this issue will happen randomly depends on the
content in
>> the  apic access page. 
>> 
>> So how should we cope with such situation? Stop emulation or,
continue
>> emulate , but access the virtual APIC page? Or any better idea?
> 
> We should stop emulation.  Probably nobody writes the TPR between the
two
> halves of a PTE write. :) 

This did happen :)

> 
> Cheers,
> 
> Tim.
> 
> --
> Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> Principal Software Engineer, Citrix Systems.
> [Company #5334508: XenSource UK Ltd, reg'd c/o EC2Y 5EB, UK.]

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel