Re: [Xen-devel] [PATCH v2 4/5] x86/msr: Handle MSR_TSC_AUX consistently for PV and HVM guests

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

> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Tuesday, November 20, 2018 10:37 PM
> 
> With PVRDTSCP mode removed, handling of MSR_TSC_AUX can move into
> the common
> code.  Move its storage into struct vcpu_msrs (dropping the HVM-specific
> msr_tsc_aux), and add an RDPID feature check as this bit also enumerates
> the
> presence of the MSR.
> 
> Introduce cpu_has_rdpid along with the synthesized cpu_has_msr_tsc_aux
> to
> correct the context switch paths, as MSR_TSC_AUX is enumerated by either
> RDTSCP or RDPID.
> 
> Drop hvm_msr_tsc_aux() entirely, and use v->arch.msrs->tsc_aux directly.
> Update hvm_load_cpu_ctxt() to check that the incoming ctxt.msr_tsc_aux
> isn't
> out of range.  In practice, no previous version of Xen ever wrote an
> out-of-range value.  Add MSR_TSC_AUX to the list of MSRs migrated for PV
> guests, but leave the HVM path using the existing space in hvm_hw_cpu.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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