Re: [Xen-devel] some questions about the HVM

[George Dunlap <dunlapg@xxxxxxxxx>]

On Fri, Mar 26, 2010 at 5:58 PM, Tim Deegan <Tim.Deegan@xxxxxxxxxx> wrote:
>> I have a question about the VMEXIT in HVM.
>> Does the behavior of modifying the pte of guest OS cause a vmexit.
>
> When using shadow pagetables, yes (more precisely, modifying a page that
> is shadowed causes a VMEXIT)

...but it's complicated.  We have an optimization called "out-of-sync"
such that modifying PTE may not cause a VMEXIT; instead, the VMEXIT
may happen when the virtual address the PTE controls is dereferenced
(akin to a TLB miss).  As Tim said, this is only in shadow mode, if
HAP (EPT or NPT) is not present / disabled.

 -George

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