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RE: [Xen-devel] [PATCH 4/4] Enable VirtualPC 2007 run on top of XEN: add_write_for_data_pages


  • To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>
  • From: "Su, Disheng" <disheng.su@xxxxxxxxx>
  • Date: Fri, 1 Feb 2008 18:06:19 +0800
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Fri, 01 Feb 2008 02:07:05 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AchktpEqLCZDZh9kRuGw+gzn+zuguwAADSfw
  • Thread-topic: [Xen-devel] [PATCH 4/4] Enable VirtualPC 2007 run on top of XEN: add_write_for_data_pages

Tim Deegan wrote:
> Hi,
> 
> At 14:24 +0800 on 01 Feb (1201875871), Su, Disheng wrote:
>> There are two cases for CR0.wp emulation: one is for page table write
>> emulation, another is for data page write emulation. We found more
>> than 100,000 page faults per second for the later case. This case
>> can be optimized by setting _PAGE_RW bit for this ReadOnly data page
>> when guest CR0.wp is 0, and remove it when CR0.wp is 1. With this
>> patch, page faults is reduced to about 10,000 at average.
> 
> Unfortunately, this isn't safe for SMP guests -- vcpu0's wp bit being
> clear shouldn't let vcpu1 ignore the _PAGE_RW bits on shared mappings.
>  
Yes, this situation havn't be handled. Could you give me some
suggestion?
How about out-of-sync shadow for CR0.wp = 0?
> Sheers,
> 
> Tim.



Best Regards,
Disheng, Su

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