Re: [RFC PATCH V3 03/16] x86/hyperv: Set Virtual Trust Level in vmbus init message

[Tianyu Lan]

On 2/1/2023 1:55 AM, Michael Kelley (LINUX) wrote:
> > index db2202d985bd..6dcbb21aac2b 100644
> > --- a/arch/x86/include/asm/hyperv-tlfs.h
> > +++ b/arch/x86/include/asm/hyperv-tlfs.h
> > @@ -36,6 +36,10 @@
> >   #define HYPERV_CPUID_MIN			0x40000005
> >   #define HYPERV_CPUID_MAX			0x4000ffff
> >
> > +/* Support for HVCALL_GET_VP_REGISTERS hvcall */
> The above comment isn't really right, in that these definitions
> aren't for the hypercall.  They are for the specific synthetic register.
>
> > +#define	HV_X64_REGISTER_VSM_VP_STATUS	0x000D0003
> > +#define HV_X64_VTL_MASK			GENMASK(3, 0)
> Hyper-V synthetic registers have two different numbering schemes.
> For registers that have synthetic MSR equivalents, there's a full list
> starting with HV_X64_MSR_GUEST_OS_ID, which defines the MSR
> address.  But these registers also have register numbers that are
> not the same as the MSR address.  These register numbers
> aren't defined anywhere in x86 Linux code because we don't access
> them using the register number.   (The register numbers*are*
> defined in ARM64 code since ARM64 doesn't have MSRs.)  But this
> register is an exception on x86.  There's no MSR equivalent so we
> must use a hypercall to fetch the value.
>
> I'd suggest starting a separate list after the definition of
> HV_X64_MSR_REFERENCE_TSC and make clear in a comment
> about the list that this is a list of register numbers, not MSR addresses.

Agree. Will update in the next version.