Re: [PATCH v2 2/8] x86/svm: silently drop writes to SYSCFG and related MSRs

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Aug 31, 2020 at 04:37:47PM +0200, Roger Pau Monné wrote:
> On Thu, Aug 27, 2020 at 05:03:50PM +0200, Jan Beulich wrote:
> > On 20.08.2020 17:08, Roger Pau Monne wrote:
> > > --- a/xen/arch/x86/hvm/svm/svm.c
> > > +++ b/xen/arch/x86/hvm/svm/svm.c
> > > @@ -1917,6 +1917,21 @@ static int svm_msr_read_intercept(unsigned int 
> > > msr, uint64_t *msr_content)
> > >              goto gpf;
> > >          break;
> > >  
> > > +    case MSR_K8_TOP_MEM1:
> > > +    case MSR_K8_TOP_MEM2:
> > > +        *msr_content = 0;
> > > +        break;
> > 
> > Any reason you don't fold this with ...
> > 
> > > +    case MSR_K8_SYSCFG:
> > > +        /*
> > > +         * Return MtrrFixDramEn: albeit the current emulated MTRR
> > > +         * implementation doesn't support the Extended Type-Field Format 
> > > having
> > > +         * such bit set is common on AMD hardware and is harmless as 
> > > long as
> > > +         * MtrrFixDramModEn isn't set.
> > > +         */
> > > +        *msr_content = K8_MTRRFIXRANGE_DRAM_ENABLE;

On the previous version you commented that returning 0 here would be
more correct, do you still think so?

I agree it seems better to not report any of those MTRR AMD specific
features, since we don't implement them in our emulated MTRR code.

Thanks, Roger.