KVM: PPC: Book3S HV Nested: Stop forwarding all HFUs to L1

If the nested hypervisor has no access to a facility because it has
been disabled by the host, it should also not be able to see the
Hypervisor Facility Unavailable that arises from one of its guests
trying to access the facility.

This patch turns a HFU that happened in L2 into a Hypervisor Emulation
Assistance interrupt and forwards it to L1 for handling. The ones that
happened because L1 explicitly disabled the facility for L2 are still
let through, along with the corresponding Cause bits in the HFSCR.

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
[np: move handling into kvmppc_handle_nested_exit]
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210811160134.904987-8-npiggin@gmail.com

arch/powerpc/kvm/book3s_hv.c

@@ -1730,6 +1730,7 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
 
 static int kvmppc_handle_nested_exit(struct kvm_vcpu *vcpu)
 {
+	struct kvm_nested_guest *nested = vcpu->arch.nested;
 	int r;
 	int srcu_idx;
 
@@ -1819,9 +1820,35 @@ static int kvmppc_handle_nested_exit(struct kvm_vcpu *vcpu)
 		fallthrough; /* go to facility unavailable handler */
 #endif
 
-	case BOOK3S_INTERRUPT_H_FAC_UNAVAIL:
-		r = RESUME_HOST;
+	case BOOK3S_INTERRUPT_H_FAC_UNAVAIL: {
+		u64 cause = vcpu->arch.hfscr >> 56;
+
+		/*
+		 * Only pass HFU interrupts to the L1 if the facility is
+		 * permitted but disabled by the L1's HFSCR, otherwise
+		 * the interrupt does not make sense to the L1 so turn
+		 * it into a HEAI.
+		 */
+		if (!(vcpu->arch.hfscr_permitted & (1UL << cause)) ||
+					(nested->hfscr & (1UL << cause))) {
+			vcpu->arch.trap = BOOK3S_INTERRUPT_H_EMUL_ASSIST;
+
+			/*
+			 * If the fetch failed, return to guest and
+			 * try executing it again.
+			 */
+			r = kvmppc_get_last_inst(vcpu, INST_GENERIC,
+						 &vcpu->arch.emul_inst);
+			if (r != EMULATE_DONE)
+				r = RESUME_GUEST;
+			else
+				r = RESUME_HOST;
+		} else {
+			r = RESUME_HOST;
+		}
+
 		break;
+	}
 
 	case BOOK3S_INTERRUPT_HV_RM_HARD:
 		vcpu->arch.trap = 0;