Re: [PATCH 0/6] Add rudimentary Hyper-V guest support

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On 18.05.2009, at 15:29, Avi Kivity wrote:

Alexander Graf wrote:

There's only a limited potential here (a factor of three, reducing 6 exits to 2, less the emulation overhead). There's a lot more to be gained from nested npt, since you'll avoid most of the original exits in the first place.

I think the reversed is the case. Look at those numbers (w2k8 bootup):

http://pastebin.ca/1423596

The only thing nested NPT would achieve is a reduction of #NPF exits. But they are absolutely in the minority today already. Normal #PF's do get directly passed to the guest already.

#NPF exits are caused when guest/host mappings change, which they don't, or by mmio (which happens both for guest and nguest).

I don't understand how you can pass #PFs directly to the guest. Surely the guest has enabled pagefault interception, and you need to set up its vmcb?

I guess you're right: http://pastebin.ca/1426458

Alex

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