linux-kernel - Re: [PATCH 2/5] KVM: SVM: Optimize nested svm msrpm merging

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Message-ID: <20100226132118.GF12689@amd.com>
Date:	Fri, 26 Feb 2010 14:21:18 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	Avi Kivity <avi@...hat.com>
CC:	Alexander Graf <agraf@...e.de>,
	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] KVM: SVM: Optimize nested svm msrpm merging

On Fri, Feb 26, 2010 at 03:10:13PM +0200, Avi Kivity wrote:
> On 02/26/2010 03:04 PM, Joerg Roedel wrote:
> >
> >>I'm still not convinced on this way of doing things. If it's static,
> >>make it static. If it's dynamic, make it dynamic. Dynamically
> >>generating a static list just sounds plain wrong to me.
> >Stop. I had a static list in the first version of the patch. This list
> >was fine except the fact that a developer needs to remember to update
> >this list if the list of non-intercepted msrs is expanded. The whole
> >reason for a dynamically built list is to take the task of maintaining
> >the list away from the developer and remove a possible source of hard to
> >find bugs. This is what the current approach does.
> 
> The problem was the two lists.  If you had a
> 
> static struct svm_direct_access_msrs = {
>     u32 index;
>     bool longmode_only;
> } direct_access_msrs = {
>    ...
> };
> 
> You could generate
> 
> static unsigned *msrpm_offsets_longmode, *msrpm_offsets_legacy;
> 
> as well as the original bitmaps at module init, no?

True for the msrs the guest always has access too. But for the lbr-msrs
the intercept bits may change at runtime. So an addtional flag is
required to indicate if the bits should be cleared initially.

	Joerg


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