Re: [PATCH v4 09/18] KVM: arm64: selftests: Add guest support to get the vcpuid

[Andrew Jones]

On Sun, Sep 12, 2021 at 12:05:22AM -0700, Reiji Watanabe wrote:
> Hi Raghu and all,
> 
> On Wed, Sep 8, 2021 at 6:38 PM Raghavendra Rao Ananta
> <rananta@xxxxxxxxxx> wrote:
> >
> > At times, such as when in the interrupt handler, the guest wants
> > to get the vcpuid that it's running on. As a result, introduce
> > get_vcpuid() that returns the vcpuid of the calling vcpu. At its
> > backend, the VMM prepares a map of vcpuid and mpidr during VM
> > initialization and exports the map to the guest for it to read.
> 
> How about using TPIDR_EL1 to hold the vcpuid ?
> i.e. have aarch64_vcpu_setup() set the register to vcpuid and
> guest_get_vcpuid() simply return a value of the register.
> This would be a simpler solution to implement.

That is a great suggestion. It's arch-specific, but maybe the
other architectures can mimic it with their own capabilities.
And, in the unlikely event a unit test wants that register for
itself, then it can build its own mpidr-vcpuid map if necessary.
Ship it :-)

Thanks,
drew