Re: [PATCH] Add Documentation/kvm/msr.txt

[Zachary Amsden]

On 05/27/2010 06:02 AM, Glauber Costa wrote:
> On Thu, May 27, 2010 at 11:15:43AM +0300, Avi Kivity wrote:
>    
> > On 05/26/2010 09:04 PM, Glauber Costa wrote:
> >      
> > > This patch adds a file that documents the usage of KVM-specific
> > > MSRs.
> > >
> > >        
> > Looks good.  A few comments:
> >
> >      
> > > +
> > > +Custom MSR list
> > > +--------
> > > +
> > > +The current supported Custom MSR list is:
> > > +
> > > +MSR_KVM_WALL_CLOCK:  0x11
> > > +
> > > +	data: physical address of a memory area.
> > >        
> > Which must be in guest RAM (i.e., don't point it somewhere random
> > and expect the hypervisor to allocate it for you).
> >
> > Must be aligned to 4 bytes (we don't enforce it though).
> >      
> I don't see the reason for it.
>
> If this is a requirement, our own implementation
> is failing to meet it.
>    

It's so the atomic write actually is atomic.  Stating a 4 -byte 
alignment requirement prevents the wall clock from crossing a page boundary.

Zach

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