Re: [PATCH 0/18][RFC] Nested Paging support for Nested SVM (akaNPT-Virtualization)

From: Marcelo Tosatti
Date: Thu Mar 04 2010 - 09:49:15 EST

On Wed, Mar 03, 2010 at 08:12:03PM +0100, Joerg Roedel wrote:
> Hi,
> here are the patches that implement nested paging support for nested
> svm. They are somewhat intrusive to the soft-mmu so I post them as RFC
> in the first round to get feedback about the general direction of the
> changes. Nevertheless I am proud to report that with these patches the
> famous kernel-compile benchmark runs only 4% slower in the l2 guest as
> in the l1 guest when l2 is single-processor. With SMP guests the
> situation is very different. The more vcpus the guest has the more is
> the performance drop from l1 to l2.
> Anyway, this post is to get feedback about the overall concept of these
> patches. Please review and give feedback :-)


What perf gain does this bring ? (i'm not aware of the current

Overall comments:

Can't you translate l2_gpa -> l1_gpa walking the current l1 nested
pagetable, and pass that to the kvm tdp fault path (with the correct
context setup)?

You probably need to include a flag in base_role to differentiate
between l1 / l2 shadow tables (say if they use the same cr3 value).

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