Re: [Xen-devel] [PATCH] xen: Fake out the Bus Unit Config MSR on revF AMD CPUs

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On Thu, 2012-03-08 at 10:14 +0000, Jan Beulich wrote:
> >>> On 07.03.12 at 18:59, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> > Win2k8 x64 reads this MSR on revF chips, where it wasn't publically
> > available; it uses a magic constant in %rdi as a password, which we
> > don't have in rdmsr_safe().  Since we'll ignore the later writes, just
> > use a plausible value here (the reset value from rev10h chips) if the
> > real CPU didn't provide one.
> > 
> > Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> > 
> > diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> > --- a/xen/arch/x86/hvm/svm/svm.c
> > +++ b/xen/arch/x86/hvm/svm/svm.c
> > @@ -1516,6 +1516,18 @@ static int svm_msr_read_intercept(unsign
> >          if ( rdmsr_safe(msr, *msr_content) == 0 )
> >              break;
> >  
> > +        if ( msr == MSR_F10_BU_CFG )
> 
> As you're aiming at revF only, shouldn't you check at least the CPU
> family here? With the MSR being model specific, you otherwise risk
> to return (bogus) data for something completely different on future
> CPU families.

I think that makes sense, but a quick glance through arch/x86/cpu/amd.c
doesn't suggest to me the most concise way of making that test... could
you give me a suggestion?

Thanks,
 -George



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