KVM: PPC: Book3S HV: Fix pending_pri value in kvmppc_xive_get_icp()

When we migrate a VM from a POWER8 host (XICS) to a POWER9 host
(XICS-on-XIVE), we have an error:

qemu-kvm: Unable to restore KVM interrupt controller state \
          (0xff000000) for CPU 0: Invalid argument

This is because kvmppc_xics_set_icp() checks the new state
is internaly consistent, and especially:

...
   1129         if (xisr == 0) {
   1130                 if (pending_pri != 0xff)
   1131                         return -EINVAL;
...

On the other side, kvmppc_xive_get_icp() doesn't set
neither the pending_pri value, nor the xisr value (set to 0)
(and kvmppc_xive_set_icp() ignores the pending_pri value)

As xisr is 0, pending_pri must be set to 0xff.

Fixes: 5af50993 ("KVM: PPC: Book3S HV: Native usage of the XIVE interrupt controller")
Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/book3s_xive.c

@@ -725,7 +725,8 @@ u64 kvmppc_xive_get_icp(struct kvm_vcpu *vcpu)
 
 	/* Return the per-cpu state for state saving/migration */
 	return (u64)xc->cppr << KVM_REG_PPC_ICP_CPPR_SHIFT |
-	       (u64)xc->mfrr << KVM_REG_PPC_ICP_MFRR_SHIFT;
+	       (u64)xc->mfrr << KVM_REG_PPC_ICP_MFRR_SHIFT |
+	       (u64)0xff << KVM_REG_PPC_ICP_PPRI_SHIFT;
 }
 
 int kvmppc_xive_set_icp(struct kvm_vcpu *vcpu, u64 icpval)