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

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Message-ID: <20100226133049.GG12689@amd.com>
Date:	Fri, 26 Feb 2010 14:30:49 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	Alexander Graf <agraf@...e.de>
CC:	Avi Kivity <avi@...hat.com>, 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 02:26:32PM +0100, Alexander Graf wrote:
> 
> On 26.02.2010, at 14:21, Joerg Roedel wrote:
> 
> > 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.
> 
> So the msrpm bitmap changes dynamically for each vcpu? Great, make it
> fully dynamic then, changing the vcpu->arch.msrpm only from within its
> vcpu context. No need for atomic ops.

The msrpm_offsets table is global. But I think I will follow Avis
suggestions and create a static direct_access_msrs list and generate the
msrpm_offsets at module_init. This solves the problem of two independent
lists too.

	Joerg


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