linux-kernel - Re: [PATCH 0/18][RFC] Nested Paging support for Nested SVM (aka NPT-Virtualization)

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Date:	Thu, 4 Mar 2010 11:42:55 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Avi Kivity <avi@...hat.com>, Alexander Graf <agraf@...e.de>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/18][RFC] Nested Paging support for Nested SVM (aka
 NPT-Virtualization)

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 :-)

Joerg,

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

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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