[PATCHv3 RFC 1/2] kvm: implement kvm_set_msi_inatomic

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

We do not want a potential broadcast to all VCPUs to run in
a host IRQ handler. Implement an API that sends an MSI
interrupt but only if it's safe from interrupt context,
that is if it is a unicast.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 include/linux/kvm_host.h |  2 ++
 virt/kvm/irq_comm.c      | 37 ++++++++++++++++++++++++++++++++-----
 2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c446435..ddb476a 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -618,6 +618,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
 int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level);
 int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
 		int irq_source_id, int level);
+int kvm_set_msi_inatomic(struct kvm_kernel_irq_routing_entry *irq_entry,
+			 struct kvm *kvm);
 void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
 void kvm_register_irq_ack_notifier(struct kvm *kvm,
 				   struct kvm_irq_ack_notifier *kian);
diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
index 5afb431..3395e03 100644
--- a/virt/kvm/irq_comm.c
+++ b/virt/kvm/irq_comm.c
@@ -114,13 +114,20 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
 	return r;
 }
 
-int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
-		struct kvm *kvm, int irq_source_id, int level)
+static bool kvm_msi_is_multicast(unsigned dest, int dest_mode)
 {
-	struct kvm_lapic_irq irq;
+	if (dest_mode == 0)
+		/* Physical mode. */
+		return dest == 0xff;
+	else
+		/* Logical mode. */
+		return dest & (dest - 1);
+}
 
-	if (!level)
-		return -1;
+static int __kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
+			 struct kvm *kvm, bool noblock)
+{
+	struct kvm_lapic_irq irq;
 
 	trace_kvm_msi_set_irq(e->msi.address_lo, e->msi.data);
 
@@ -134,10 +141,30 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
 	irq.level = 1;
 	irq.shorthand = 0;
 
+	/* Multicast MSI doesn't really block but might take a long time. */
+	if (unlikely(noblock && kvm_msi_is_multicast(irq.dest_id,
+						     irq.delivery_mode)))
+		return -EWOULDBLOCK;
+
 	/* TODO Deal with RH bit of MSI message address */
 	return kvm_irq_delivery_to_apic(kvm, NULL, &irq);
 }
 
+int kvm_set_msi_inatomic(struct kvm_kernel_irq_routing_entry *e,
+			 struct kvm *kvm)
+{
+	return __kvm_set_msi(e, kvm, true);
+}
+
+int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
+			 struct kvm *kvm, int irq_source_id, int level)
+{
+	if (unlikely(!level))
+		return -1;
+
+	return __kvm_set_msi(e, kvm, false);
+}
+
 int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi)
 {
 	struct kvm_kernel_irq_routing_entry route;
-- 
MST

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html