KVM: arm64: selftests: Add guest support to get the vcpuid

At times, such as when in the interrupt handler, the guest wants
to get the vcpuid that it's running on to pull the per-cpu private
data. As a result, introduce guest_get_vcpuid() that returns the
vcpuid of the calling vcpu. The interface is architecture
independent, but defined only for arm64 as of now.
Suggested-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Reviewed-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211007233439.1826892-11-rananta@google.com

tools/testing/selftests/kvm/include/kvm_util.h

@@ -400,4 +400,6 @@ uint64_t get_ucall(struct kvm_vm *vm, uint32_t vcpu_id, struct ucall *uc);
 int vm_get_stats_fd(struct kvm_vm *vm);
 int vcpu_get_stats_fd(struct kvm_vm *vm, uint32_t vcpuid);
 
+uint32_t guest_get_vcpuid(void);
+
 #endif /* SELFTEST_KVM_UTIL_H */

tools/testing/selftests/kvm/lib/aarch64/processor.c

@@ -277,6 +277,7 @@ void aarch64_vcpu_setup(struct kvm_vm *vm, uint32_t vcpuid, struct kvm_vcpu_init
 	set_reg(vm, vcpuid, KVM_ARM64_SYS_REG(SYS_TCR_EL1), tcr_el1);
 	set_reg(vm, vcpuid, KVM_ARM64_SYS_REG(SYS_MAIR_EL1), DEFAULT_MAIR_EL1);
 	set_reg(vm, vcpuid, KVM_ARM64_SYS_REG(SYS_TTBR0_EL1), vm->pgd);
+	set_reg(vm, vcpuid, KVM_ARM64_SYS_REG(SYS_TPIDR_EL1), vcpuid);
 }
 
 void vcpu_dump(FILE *stream, struct kvm_vm *vm, uint32_t vcpuid, uint8_t indent)
@@ -426,3 +427,8 @@ void vm_install_exception_handler(struct kvm_vm *vm, int vector,
 	assert(vector < VECTOR_NUM);
 	handlers->exception_handlers[vector][0] = handler;
 }
+
+uint32_t guest_get_vcpuid(void)
+{
+	return read_sysreg(tpidr_el1);
+}