[Qemu-devel] [RFC PATCH 18/34] hyperv: add support for KVM_HYPERV_EVENTFD

[Roman Kagan]

When setting up a notifier for Hyper-V event connection, attempt to use
the KVM-assisted one first, and fall back to userspace handling of the
hypercall if the kernel doesn't provide the requested feature.

Signed-off-by: Roman Kagan <address@hidden>
---
 include/sysemu/kvm.h |  1 +
 accel/kvm/kvm-all.c  | 15 +++++++++++++++
 target/i386/hyperv.c | 21 ++++++++++++++++++++-
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index bbf12a1723..70ad0a54b7 100644
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -496,6 +496,7 @@ void kvm_irqchip_set_qemuirq_gsi(KVMState *s, qemu_irq irq, 
int gsi);
 void kvm_pc_gsi_handler(void *opaque, int n, int level);
 void kvm_pc_setup_irq_routing(bool pci_enabled);
 void kvm_init_irq_routing(KVMState *s);
+int kvm_set_hv_event_notifier(KVMState *s, uint32_t conn_id, EventNotifier *n);
 
 /**
  * kvm_arch_irqchip_create:
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index f290f487a5..c3ba87b701 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1423,6 +1423,21 @@ static void kvm_irqchip_create(MachineState *machine, 
KVMState *s)
     s->gsimap = g_hash_table_new(g_direct_hash, g_direct_equal);
 }
 
+int kvm_set_hv_event_notifier(KVMState *s, uint32_t conn_id, EventNotifier *n)
+{
+    struct kvm_hyperv_eventfd hvevfd = {
+        .conn_id = conn_id,
+        .fd = n ? event_notifier_get_fd(n) : -1,
+        .flags = n ? 0 : KVM_HYPERV_EVENTFD_DEASSIGN,
+    };
+
+    if (!kvm_check_extension(s, KVM_CAP_HYPERV_EVENTFD)) {
+        return -ENOSYS;
+    }
+
+    return kvm_vm_ioctl(s, KVM_HYPERV_EVENTFD, &hvevfd);
+}
+
 /* Find number of supported CPUs using the recommended
  * procedure from the kernel API documentation to cope with
  * older kernels that may be missing capabilities.
diff --git a/target/i386/hyperv.c b/target/i386/hyperv.c
index e43cbb9322..63dcb23fa8 100644
--- a/target/i386/hyperv.c
+++ b/target/i386/hyperv.c
@@ -313,7 +313,8 @@ unlock:
     return ret;
 }
 
-int hyperv_set_evt_notifier(uint32_t conn_id, EventNotifier *notifier)
+static int hyperv_set_evt_notifier_userspace(uint32_t conn_id,
+                                             EventNotifier *notifier)
 {
     int ret;
     EvtHandler *eh;
@@ -346,6 +347,24 @@ unlock:
     return ret;
 }
 
+static bool hv_evt_notifier_userspace;
+
+int hyperv_set_evt_notifier(uint32_t conn_id, EventNotifier *notifier)
+{
+    if (!hv_evt_notifier_userspace) {
+        int ret = kvm_set_hv_event_notifier(kvm_state, conn_id, notifier);
+        if (ret != -ENOSYS) {
+            return ret;
+        }
+
+        hv_evt_notifier_userspace = true;
+        warn_report("Hyper-V event signaling in KVM not supported; "
+                    "using slower userspace hypercall processing");
+    }
+
+    return hyperv_set_evt_notifier_userspace(conn_id, notifier);
+}
+
 static uint64_t hvcall_post_message(uint64_t param, bool fast)
 {
     uint64_t ret;
-- 
2.14.3