KVM: Add support to disable MSI for assigned device

MSI is always enabled by default for msi2intx=1. But if msi2intx=0, we
have to disable MSI if guest require to do so.

The patch also discard unnecessary msi2intx judgment if guest want to update
MSI state.

Notice KVM_DEV_IRQ_ASSIGN_MSI_ACTION is a mask which should cover all MSI
related operations, though we only got one for now.
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

include/linux/kvm.h

@@ -550,6 +550,7 @@ struct kvm_assigned_irq {
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 
+#define KVM_DEV_IRQ_ASSIGN_MSI_ACTION	KVM_DEV_IRQ_ASSIGN_ENABLE_MSI
 #define KVM_DEV_IRQ_ASSIGN_ENABLE_MSI	(1 << 0)
 
 #endif

virt/kvm/kvm_main.c

@@ -343,6 +343,14 @@ static int assigned_device_update_msi(struct kvm *kvm,
 		adev->irq_requested_type &= ~KVM_ASSIGNED_DEV_GUEST_MSI;
 		adev->guest_irq = airq->guest_irq;
 		adev->ack_notifier.gsi = airq->guest_irq;
+	} else {
+		/*
+		 * Guest require to disable device MSI, we disable MSI and
+		 * re-enable INTx by default again. Notice it's only for
+		 * non-msi2intx.
+		 */
+		assigned_device_update_intx(kvm, adev, airq);
+		return 0;
 	}
 
 	if (adev->irq_requested_type & KVM_ASSIGNED_DEV_HOST_MSI)
@@ -379,6 +387,7 @@ static int kvm_vm_ioctl_assign_irq(struct kvm *kvm,
 {
 	int r = 0;
 	struct kvm_assigned_dev_kernel *match;
+	u32 current_flags = 0, changed_flags;
 
 	mutex_lock(&kvm->lock);
 
@@ -416,8 +425,13 @@ static int kvm_vm_ioctl_assign_irq(struct kvm *kvm,
 		}
 	}
 
-	if ((!msi2intx &&
-	     (assigned_irq->flags & KVM_DEV_IRQ_ASSIGN_ENABLE_MSI)) ||
+	if ((match->irq_requested_type & KVM_ASSIGNED_DEV_HOST_MSI) &&
+		 (match->irq_requested_type & KVM_ASSIGNED_DEV_GUEST_MSI))
+		current_flags |= KVM_DEV_IRQ_ASSIGN_ENABLE_MSI;
+
+	changed_flags = assigned_irq->flags ^ current_flags;
+
+	if ((changed_flags & KVM_DEV_IRQ_ASSIGN_MSI_ACTION) ||
 	    (msi2intx && match->dev->msi_enabled)) {
 #ifdef CONFIG_X86
 		r = assigned_device_update_msi(kvm, match, assigned_irq);