kvm tools: Prepare support for VIRTIO_RING_F_EVENT_IDX

This patch is the base for enabling support for event index feature in the virtio spec.
We do so by updating and evaluating the used/avail event idx in the virtio ring functions.

Actual usage of this flag is in the following patches.

The results are less notifications between the guest and host, and in
result faster operation of the virt queues.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --git a/tools/kvm/include/kvm/virtio.h b/tools/kvm/include/kvm/virtio.h
index c6c380d3e500293613ab08e591653bf6dd7c1e7a..cd24285390bc2cee24f380fa1d862bf70b5be7e5 100644 (file)
--- a/tools/kvm/include/kvm/virtio.h
+++ b/tools/kvm/include/kvm/virtio.h
@@ -38,6 +38,8 @@ static inline bool virt_queue__available(struct virt_queue *vq)
 {
        if (!vq->vring.avail)
                return 0;
+
+       vring_avail_event(&vq->vring) = vq->last_avail_idx;
        return vq->vring.avail->idx !=  vq->last_avail_idx;
 }
 
@@ -51,6 +53,11 @@ static inline void *guest_pfn_to_host(struct kvm *kvm, u32 pfn)
        return guest_flat_to_host(kvm, (unsigned long)pfn << VIRTIO_PCI_QUEUE_ADDR_SHIFT);
 }
 
+static inline int virtio_queue__should_signal(struct virt_queue *vq)
+{
+       return vring_used_event(&vq->vring) <= vq->vring.used->idx;
+}
+
 struct vring_used_elem *virt_queue__set_used_elem(struct virt_queue *queue, u32 head, u32 len);
 
 u16 virt_queue__get_iov(struct virt_queue *queue, struct iovec iov[], u16 *out, u16 *in, struct kvm *kvm);