arm_gic_kvm: Tell kernel about number of IRQs

Newer kernels support a device attribute on the GIC which allows us to
tell it how many IRQs this GIC instance is configured with; use it, if
it exists.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NChristoffer Dall <christoffer.dall@linaro.org>
Message-id: 1417718679-1071-1-git-send-email-peter.maydell@linaro.org

hw/intc/arm_gic_kvm.c

@@ -92,6 +92,21 @@ static bool kvm_arm_gic_can_save_restore(GICState *s)
     return s->dev_fd >= 0;
 }
 
+static bool kvm_gic_supports_attr(GICState *s, int group, int attrnum)
+{
+    struct kvm_device_attr attr = {
+        .group = group,
+        .attr = attrnum,
+        .flags = 0,
+    };
+
+    if (s->dev_fd == -1) {
+        return false;
+    }
+
+    return kvm_device_ioctl(s->dev_fd, KVM_HAS_DEVICE_ATTR, &attr) == 0;
+}
+
 static void kvm_gic_access(GICState *s, int group, int offset,
                                    int cpu, uint32_t *val, bool write)
 {
@@ -553,6 +568,11 @@ static void kvm_arm_gic_realize(DeviceState *dev, Error **errp)
         return;
     }
 
+    if (kvm_gic_supports_attr(s, KVM_DEV_ARM_VGIC_GRP_NR_IRQS, 0)) {
+        uint32_t numirqs = s->num_irq;
+        kvm_gic_access(s, KVM_DEV_ARM_VGIC_GRP_NR_IRQS, 0, 0, &numirqs, 1);
+    }
+
     /* Distributor */
     memory_region_init_reservation(&s->iomem, OBJECT(s),
                                    "kvm-gic_dist", 0x1000);