* some questions about the HVM
@ 2010-03-26 14:00 WangWei王伟
2010-03-26 16:58 ` Tim Deegan
0 siblings, 1 reply; 3+ messages in thread
From: WangWei王伟 @ 2010-03-26 14:00 UTC (permalink / raw)
To: xen-devel
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Hi all,
I have a question about the VMEXIT in HVM.
Does the behavior of modifying the pte of guest OS cause a vmexit.
If so ,the vmexit reason is page fault or something else ?
Look forward to you help!
Thanks!
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: some questions about the HVM
2010-03-26 14:00 some questions about the HVM WangWei王伟
@ 2010-03-26 16:58 ` Tim Deegan
2010-03-30 9:57 ` George Dunlap
0 siblings, 1 reply; 3+ messages in thread
From: Tim Deegan @ 2010-03-26 16:58 UTC (permalink / raw)
To: WangWei????; +Cc: xen-devel
Hi,
At 14:00 +0000 on 26 Mar (1269612028), WangWei???? 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). When using hardware-assisted paging (NPT
or EPT), no.
> If so ,the vmexit reason is page fault or something else ?
It's a page fault, because shadowed pages are always mapped read-only in
the shadow page tables.
Why do you want to know?
Cheers,
Tim.
--
Tim Deegan <Tim.Deegan@citrix.com>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: some questions about the HVM
2010-03-26 16:58 ` Tim Deegan
@ 2010-03-30 9:57 ` George Dunlap
0 siblings, 0 replies; 3+ messages in thread
From: George Dunlap @ 2010-03-30 9:57 UTC (permalink / raw)
To: Tim Deegan; +Cc: xen-devel, WangWei????
On Fri, Mar 26, 2010 at 5:58 PM, Tim Deegan <Tim.Deegan@citrix.com> 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
^ permalink raw reply [flat|nested] 3+ messages in thread
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2010-03-26 14:00 some questions about the HVM WangWei王伟
2010-03-26 16:58 ` Tim Deegan
2010-03-30 9:57 ` George Dunlap
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