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! _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/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) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
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 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel