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RE: [Xen-devel] write page table in user mode

To: "Michael A Fetterman" <Michael.Fetterman@xxxxxxxxxxxx>, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>
Subject: RE: [Xen-devel] write page table in user mode
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Mon, 4 Feb 2008 21:37:55 +0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, "Su, Disheng" <disheng.su@xxxxxxxxx>
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Thread-topic: [Xen-devel] write page table in user mode
>From: Michael A Fetterman
>Sent: 2008年2月4日 20:02
>> > > It's said to be a forward progress issue, that 
>instruction page of faulting
>> > > IP falls into mapped virtual range by same L1 as the 
>target frame it tries
>> > > to update. So the implication is that the unshadow unfortunately
>> > > succeeds.
>> Do you mean that the guest instruction stream is changing 
>the VM mapping
>> of the page under %eip, from user-space?  Wow.
>When I first read Kevin's description, I took it to mean that 
>the same L1 *page*
>(not entry) was mapping the current EIP and the target of the 
>write.  If this is
>case, then the current code's prefetching of L1 entries on the 
>same page is
>probably interacting with the user-space write heuristic, causing the
>shadow->unshadow->shadow livelock, making for a much easier fix.

Yes, same L1 page. Sorry for confusion. It may be some map-cache-
like usage within same 4M virtual range including code itself. But
I'm not clear about what you mean as a 'much easier' fix. Could you


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