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

To: "Su, Disheng" <disheng.su@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 4/4] Enable VirtualPC 2007 run on top of XEN: add_write_for_data_pages
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Fri, 1 Feb 2008 09:40:17 +0000
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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. 



Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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