[PATCH 1/2] KVM: not register a IRQ bypass producer if unsupported or disabled

[Zhenzhong Duan <zhenzhong.duan@gmail.com>]

If Post interrupt is disabled due to hardware limit or forcely disabled
by "intremap=nopost" parameter, return -EINVAL so that the legacy mode IRQ
isn't registered as IRQ bypass producer.

With this change, below message is printed:
"vfio-pci 0000:db:00.0: irq bypass producer (token 0000000060c8cda5) registration fails: -22"

..which also hints us if a vfio or vdpa device works in PI mode or legacy
remapping mode.

Add a print to vdpa code just like what vfio_msi_set_vector_signal() does.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@gmail.com>
---
 arch/x86/kvm/svm/avic.c | 3 +--
 arch/x86/kvm/vmx/vmx.c  | 5 ++---
 drivers/vhost/vdpa.c    | 5 +++++
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index ac830cd..316142a 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -814,7 +814,7 @@ int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
 
 	if (!kvm_arch_has_assigned_device(kvm) ||
 	    !irq_remapping_cap(IRQ_POSTING_CAP))
-		return 0;
+		return ret;
 
 	pr_debug("SVM: %s: host_irq=%#x, guest_irq=%#x, set=%#x\n",
 		 __func__, host_irq, guest_irq, set);
@@ -899,7 +899,6 @@ int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
 		}
 	}
 
-	ret = 0;
 out:
 	srcu_read_unlock(&kvm->irq_srcu, idx);
 	return ret;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f0a9954..1fed6d6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7716,12 +7716,12 @@ static int vmx_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
 	struct kvm_lapic_irq irq;
 	struct kvm_vcpu *vcpu;
 	struct vcpu_data vcpu_info;
-	int idx, ret = 0;
+	int idx, ret = -EINVAL;
 
 	if (!kvm_arch_has_assigned_device(kvm) ||
 		!irq_remapping_cap(IRQ_POSTING_CAP) ||
 		!kvm_vcpu_apicv_active(kvm->vcpus[0]))
-		return 0;
+		return ret;
 
 	idx = srcu_read_lock(&kvm->irq_srcu);
 	irq_rt = srcu_dereference(kvm->irq_routing, &kvm->irq_srcu);
@@ -7787,7 +7787,6 @@ static int vmx_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
 		}
 	}
 
-	ret = 0;
 out:
 	srcu_read_unlock(&kvm->irq_srcu, idx);
 	return ret;
diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 62a9bb0..b20060a 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -107,6 +107,11 @@ static void vhost_vdpa_setup_vq_irq(struct vhost_vdpa *v, u16 qid)
 	vq->call_ctx.producer.token = vq->call_ctx.ctx;
 	vq->call_ctx.producer.irq = irq;
 	ret = irq_bypass_register_producer(&vq->call_ctx.producer);
+	if (unlikely(ret))
+		dev_info(&vdpa->dev,
+		"irq bypass producer (token %p) registration fails: %d\n",
+		vq->call_ctx.producer.token, ret);
+
 	spin_unlock(&vq->call_ctx.ctx_lock);
 }
 
-- 
1.8.3.1