Re: [PATCH v3 3/3] Add support for RAPL MSRs in KVM/Qemu

[Anthony Harivel]

Daniel P. Berrangé, Jan 29, 2024 at 20:29:
> On Thu, Jan 25, 2024 at 08:22:14AM +0100, Anthony Harivel wrote:
> > diff --git a/docs/specs/rapl-msr.rst b/docs/specs/rapl-msr.rst
> > new file mode 100644
> > index 000000000000..04d27c198fc0
> > --- /dev/null
> > +++ b/docs/specs/rapl-msr.rst
> > @@ -0,0 +1,133 @@
> > +================
> > +RAPL MSR support
> > +================
>
> > +
> > +Current Limitations
> > +-------------------
> > +
> > +- Works only on Intel host CPUs because AMD CPUs are using different MSR
> > +  addresses.
>
> The privileged helper program is validating an allow list of MSRs.
>
> If those MSRs are only correct on Intel hosts, then the validation
> is incomplete, and it could be allowing unprivileged processes on
> AMD hosts to access forbidden MSRS whose address happen to clash
> with the Intel RAPL MSRs.
>
> IOW, the privileged helper needs to call cpuid() and validate that
> the current host vendor is Intel.
>
> I suspect we also need a feature check of some kind to validate
> that the intel processor supports this features, since old ones
> definitely didn't, and we shouldn't assume all future ones will
> either.
>

To validate that the processor supports the RAPL feature I propose
to check this on the Host:

$ cat /sys/class/powercap/intel-rapl/enabled
1


The only down side is that INTEL RAPL drivers needs to be
mounted then. We don't need it because we directly read the MSRs.

Regards,
Anthony