在 2022/9/1 13:54, Guo Zhi 写道:
Follow VIRTIO 1.1 spec, only writing out a single used ring for a batch
of descriptors.
Signed-off-by: Guo Zhi <qtxuning1999@xxxxxxxxxxx>
---
drivers/vhost/vhost.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 40097826cff0..26862c8bf751 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2376,10 +2376,20 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
vring_used_elem_t __user *used;
u16 old, new;
int start;
+ int copy_n = count;
+ /**
+ * If in order feature negotiated, devices can notify the use of a batch of buffers to
+ * the driver by only writing out a single used ring entry with the id corresponding
+ * to the head entry of the descriptor chain describing the last buffer in the batch.
+ */
+ if (vhost_has_feature(vq, VIRTIO_F_IN_ORDER)) {
+ copy_n = 1;
+ heads = &heads[count - 1];
+ }
Would it better to have a dedicated helper like
vhost_add_used_in_order() here?
start = vq->last_used_idx & (vq->num - 1);
used = vq->used->ring + start;
- if (vhost_put_used(vq, heads, start, count)) {
+ if (vhost_put_used(vq, heads, start, copy_n)) {
vq_err(vq, "Failed to write used");
return -EFAULT;
}
@@ -2388,7 +2398,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
smp_wmb();
/* Log used ring entry write. */
log_used(vq, ((void __user *)used - (void __user *)vq->used),
- count * sizeof *used);
+ copy_n * sizeof(*used));
}
old = vq->last_used_idx;
new = (vq->last_used_idx += count);
@@ -2410,7 +2420,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
start = vq->last_used_idx & (vq->num - 1);
n = vq->num - start;
- if (n < count) {
+ if (n < count && !vhost_has_feature(vq, VIRTIO_F_IN_ORDER)) {
This seems strange, any reason for this? (Actually if we support
in-order we only need one used slot which fit for the case here)
Thanks
r = __vhost_add_used_n(vq, heads, n);
if (r < 0)
return r;
