KVM: arm/arm64: vgic-irqfd: Implement kvm_arch_set_irq_inatomic

Now that we have a cache of MSI->LPI translations, it is pretty
easy to implement kvm_arch_set_irq_inatomic (this cache can be
parsed without sleeping).

Hopefully, this will improve some LPI-heavy workloads.
Tested-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

virt/kvm/arm/vgic/vgic-irqfd.c

@@ -66,6 +66,15 @@ int kvm_set_routing_entry(struct kvm *kvm,
 	return r;
 }
 
+static void kvm_populate_msi(struct kvm_kernel_irq_routing_entry *e,
+			     struct kvm_msi *msi)
+{
+	msi->address_lo = e->msi.address_lo;
+	msi->address_hi = e->msi.address_hi;
+	msi->data = e->msi.data;
+	msi->flags = e->msi.flags;
+	msi->devid = e->msi.devid;
+}
 /**
  * kvm_set_msi: inject the MSI corresponding to the
  * MSI routing entry
@@ -79,21 +88,36 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
 {
 	struct kvm_msi msi;
 
-	msi.address_lo = e->msi.address_lo;
-	msi.address_hi = e->msi.address_hi;
-	msi.data = e->msi.data;
-	msi.flags = e->msi.flags;
-	msi.devid = e->msi.devid;
-
 	if (!vgic_has_its(kvm))
 		return -ENODEV;
 
 	if (!level)
 		return -1;
 
+	kvm_populate_msi(e, &msi);
 	return vgic_its_inject_msi(kvm, &msi);
 }
 
+/**
+ * kvm_arch_set_irq_inatomic: fast-path for irqfd injection
+ *
+ * Currently only direct MSI injection is supported.
+ */
+int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
+			      struct kvm *kvm, int irq_source_id, int level,
+			      bool line_status)
+{
+	if (e->type == KVM_IRQ_ROUTING_MSI && vgic_has_its(kvm) && level) {
+		struct kvm_msi msi;
+
+		kvm_populate_msi(e, &msi);
+		if (!vgic_its_inject_cached_translation(kvm, &msi))
+			return 0;
+	}
+
+	return -EWOULDBLOCK;
+}
+
 int kvm_vgic_setup_default_irq_routing(struct kvm *kvm)
 {
 	struct kvm_irq_routing_entry *entries;