On Sun, Jul 11, 2010, Avi Kivity wrote about "Re: [PATCH 0/24] Nested VMX, v5": > >nesting- > >aware L1 guest hypervisors to actually use that internal structure to > >modify > >vmcs12 directly, without vmread/vmwrite and exits. > > > > No, they can't, since (for writes) L0 might cache the information and > not read it again. For reads, L0 might choose to update vmcs12 on demand. Well, in the current version of the nested code, all L0 does on a L1 vmwrite is to update the in-memory vmcs12 structure. It doesn't not update vmcs02, nor cache anything, nor remember what has changed and what hasn't. So replacing it with a direct write to the memory structure should be fine... Of course, this situation isn't optimal, and we *should* optimize the number of unnecessary vmwrites L2 entry and exit (and we actually tried some of this in our tech report), but it's not in the current patch set. When we do these kind of optimizations, you're right that: > A pvvmread/write needs to communicate with L0 about what fields are > valid (likely using available and dirty bitmaps). -- Nadav Har'El | Sunday, Jul 11 2010, 1 Av 5770 nyh@xxxxxxxxxxxxxxxxxxx |----------------------------------------- Phone +972-523-790466, ICQ 13349191 |If marriage was illegal, only outlaws http://nadav.harel.org.il |would have in-laws. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
