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Re: [Xen-devel] [Q] guest and user protection on x86-64 by paging

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Subject: Re: [Xen-devel] [Q] guest and user protection on x86-64 by paging
From: Min Lee <min.lee@xxxxxxxxxx>
Date: Mon, 02 Aug 2010 10:35:18 -0400
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I see..
Thanks for your help, Jeremy.

On 8/2/2010 2:31 AM, Jeremy Fitzhardinge wrote:
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.


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