kvm: Decouple 'MSI routing via irqfds' from 'kernel irqchip'

Decouple another x86-specific assumption about what irqchips imply.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Avi Kivity <avi@redhat.com>

hw/virtio-pci.c

@@ -627,7 +627,7 @@ static int virtio_pci_set_guest_notifiers(void *opaque, bool assign)
     int r, n;
 
     /* Must unset vector notifier while guest notifier is still assigned */
-    if (kvm_irqchip_in_kernel() && !assign) {
+    if (kvm_msi_via_irqfd_enabled() && !assign) {
         msix_unset_vector_notifiers(&proxy->pci_dev);
         g_free(proxy->vector_irqfd);
         proxy->vector_irqfd = NULL;
@@ -645,7 +645,7 @@ static int virtio_pci_set_guest_notifiers(void *opaque, bool assign)
     }
 
     /* Must set vector notifier after guest notifier has been assigned */
-    if (kvm_irqchip_in_kernel() && assign) {
+    if (kvm_msi_via_irqfd_enabled() && assign) {
         proxy->vector_irqfd =
             g_malloc0(sizeof(*proxy->vector_irqfd) *
                       msix_nr_vectors_allocated(&proxy->pci_dev));

kvm-all.c

@@ -102,6 +102,7 @@ KVMState *kvm_state;
 bool kvm_kernel_irqchip;
 bool kvm_async_interrupts_allowed;
 bool kvm_irqfds_allowed;
+bool kvm_msi_via_irqfd_allowed;
 
 static const KVMCapabilityInfo kvm_required_capabilites[] = {
     KVM_CAP_INFO(USER_MEMORY),

kvm-stub.c

@@ -21,6 +21,7 @@ KVMState *kvm_state;
 bool kvm_kernel_irqchip;
 bool kvm_async_interrupts_allowed;
 bool kvm_irqfds_allowed;
+bool kvm_msi_via_irqfd_allowed;
 
 int kvm_init_vcpu(CPUArchState *env)
 {

kvm.h

@@ -26,6 +26,7 @@ extern int kvm_allowed;
 extern bool kvm_kernel_irqchip;
 extern bool kvm_async_interrupts_allowed;
 extern bool kvm_irqfds_allowed;
+extern bool kvm_msi_via_irqfd_allowed;
 
 #if defined CONFIG_KVM || !defined NEED_CPU_H
 #define kvm_enabled()           (kvm_allowed)
@@ -50,11 +51,21 @@ extern bool kvm_irqfds_allowed;
  */
 #define kvm_irqfds_enabled() (kvm_irqfds_allowed)
 
+/**
+ * kvm_msi_via_irqfd_enabled:
+ *
+ * Returns: true if we can route a PCI MSI (Message Signaled Interrupt)
+ * to a KVM CPU via an irqfd. This requires that the kernel supports
+ * this and that we're running in a configuration that permits it.
+ */
+#define kvm_msi_via_irqfd_enabled() (kvm_msi_via_irqfd_allowed)
+
 #else
 #define kvm_enabled()           (0)
 #define kvm_irqchip_in_kernel() (false)
 #define kvm_async_interrupts_enabled() (false)
 #define kvm_irqfds_enabled() (false)
+#define kvm_msi_via_irqfd_enabled() (false)
 #endif
 
 struct kvm_run;

target-i386/kvm.c

@@ -2048,7 +2048,9 @@ void kvm_arch_init_irq_routing(KVMState *s)
         no_hpet = 1;
     }
     /* We know at this point that we're using the in-kernel
-     * irqchip, so we can use irqfds.
+     * irqchip, so we can use irqfds, and on x86 we know
+     * we can use msi via irqfd.
      */
     kvm_irqfds_allowed = true;
+    kvm_msi_via_irqfd_allowed = true;
 }