Re: [Xen-devel] [ping] Re: [PATCH 2/5] x86/pv: Avoid leaking other guests' MSR_TSC_AUX values into PV context

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Tuesday, February 27, 2018 3:11 AM
> 
> On 26/02/18 11:25, Jan Beulich wrote:
> >>>> On 20.02.18 at 12:58, <andrew.cooper3@xxxxxxxxxx> wrote:
> >> If the CPU pipeline supports RDTSCP or RDPID, a guest can observe the
> value in
> >> MSR_TSC_AUX, irrespective of whether the relevant CPUID features are
> >> advertised/hidden.
> >>
> >> At the moment, paravirt_ctxt_switch_to() only writes to MSR_TSC_AUX if
> >> TSC_MODE_PVRDTSCP mode is enabled, but this is not the default mode.
> >> Therefore, default PV guests can read the value from a previously
> scheduled
> >> HVM vcpu, or TSC_MODE_PVRDTSCP-enabled PV guest.
> >>
> >> Alter the PV path to always write to MSR_TSC_AUX, using 0 in the
> common
> >> case.
> >>
> >> To amortise overhead cost, introduce wrmsr_tsc_aux() which performs
> a lazy
> >> update of the MSR, and use this function consistently across the
> codebase.
> >>
> >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > Despite me continuing to think that RDTSCP and RDPID should be
> > fully independent features, this being in line with the SDM:
> > Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Thanks.
> 
> Given the important of this patch, I feel it is time to ping the VT-x
> and SVM maintainers for their input.
> 
> ~Andrew

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
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