KVM: arm64: Let errors from SMCCC emulation to reach userspace

Typically a negative return from an exit handler is used to request a
return to userspace with the specified error. KVM's handling of SMCCC
emulation (i.e. both HVCs and SMCs) deviates from the trend and resumes
the guest instead.

Stop handling negative returns this way and instead let the error
percolate to userspace.
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230404154050.2270077-12-oliver.upton@linux.dev

arch/arm64/kvm/handle_exit.c

@@ -36,8 +36,6 @@ static void kvm_handle_guest_serror(struct kvm_vcpu *vcpu, u64 esr)
 
 static int handle_hvc(struct kvm_vcpu *vcpu)
 {
-	int ret;
-
 	trace_kvm_hvc_arm64(*vcpu_pc(vcpu), vcpu_get_reg(vcpu, 0),
 			    kvm_vcpu_hvc_get_imm(vcpu));
 	vcpu->stat.hvc_exit_stat++;
@@ -52,19 +50,11 @@ static int handle_hvc(struct kvm_vcpu *vcpu)
 		return 1;
 	}
 
-	ret = kvm_smccc_call_handler(vcpu);
-	if (ret < 0) {
-		vcpu_set_reg(vcpu, 0, ~0UL);
-		return 1;
-	}
-
-	return ret;
+	return kvm_smccc_call_handler(vcpu);
 }
 
 static int handle_smc(struct kvm_vcpu *vcpu)
 {
-	int ret;
-
 	/*
 	 * "If an SMC instruction executed at Non-secure EL1 is
 	 * trapped to EL2 because HCR_EL2.TSC is 1, the exception is a
@@ -93,11 +83,7 @@ static int handle_smc(struct kvm_vcpu *vcpu)
 	 * at Non-secure EL1 is trapped to EL2 if HCR_EL2.TSC==1, rather than
 	 * being treated as UNDEFINED.
 	 */
-	ret = kvm_smccc_call_handler(vcpu);
-	if (ret < 0)
-		vcpu_set_reg(vcpu, 0, ~0UL);
-
-	return ret;
+	return kvm_smccc_call_handler(vcpu);
 }
 
 /*