KVM: PPC: Book3S HV nestedv2: Do not cancel pending decrementer exception

In the nestedv2 case, if there is a pending decrementer exception, the
L1 must get the L2's timebase from the L0 to see if the exception should
be cancelled. This adds the overhead of a H_GUEST_GET_STATE call to the
likely case in which the decrementer should not be cancelled.

Avoid this logic for the nestedv2 case.
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231201132618.555031-13-vaibhav@linux.ibm.com

arch/powerpc/kvm/book3s_hv.c

@@ -4834,7 +4834,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
 	 * entering a nested guest in which case the decrementer is now owned
 	 * by L2 and the L1 decrementer is provided in hdec_expires
 	 */
-	if (kvmppc_core_pending_dec(vcpu) &&
+	if (!kvmhv_is_nestedv2() && kvmppc_core_pending_dec(vcpu) &&
 			((tb < kvmppc_dec_expires_host_tb(vcpu)) ||
 			 (trap == BOOK3S_INTERRUPT_SYSCALL &&
 			  kvmppc_get_gpr(vcpu, 3) == H_ENTER_NESTED)))