linux-kernel - Re: [PATCH 0/6] KVM: SVM: Wrap access to intercept masks into functions

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Date:	Wed, 1 Dec 2010 11:34:19 +0100
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/6] KVM: SVM: Wrap access to intercept masks into
 functions

On Tue, Nov 30, 2010 at 12:42:28PM -0500, Avi Kivity wrote:
> On 11/30/2010 07:03 PM, Joerg Roedel wrote:
> > Hi Avi, Hi Marcelo,
> >
> > this patchset wraps the access to the intercept vectors in the VMCB into
> > specific functions. There are two reasons for this:
> >
> > 	1) In the nested-svm code the effective intercept masks are
> > 	   calculated from the host and the guest intercept masks.
> > 	   Whenever KVM changes the host intercept mask while the VCPU
> > 	   is in guest-mode the effective intercept masks need to be
> > 	   re-calculated. This is nicely wrapped into these functions
> > 	   now and makes the code more robust.
> >
> > 	2) These changes make the implementation of the upcoming
> > 	   vmcb-clean-bits feature easier and also more robust (which
> > 	   was the main reason for writing this patchset).
> >
> > These patches were developed on-top of the patch-set I sent yesterday. I
> > tested these patches with various guests (Windows-64, Linux 32,32e and
> > 64 as well as with nested-svm).
> >
> 
> Looks good.
> 
> One potential issue is that a series of set_intercept()s causes 
> recalc_intercepts() to be called multiple times.  If it turns out to be 
> a problem, we can fix it by having an intercepts dirty bit and 
> recalculating during guest entry if the bit is set.
> 
> Since it's nested svm only, I doubt we'll see a problem in the short term.

Yes, we can optimize it if it turns out to be a problem. I thought that
these changes happen infrequently enough and that there should be no
more than 2-3 bits changed per exit-entry cycle at all.

	Joerg

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