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

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
[off-list ref] wrote:

quoted

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