Re: [Qemu-devel] [PATCH v2 3/6] vhost: extend ring information update for IOTLB to all rings

[Michael S. Tsirkin]

On Fri, May 26, 2017 at 04:28:55PM +0200, Maxime Coquelin wrote:
> Vhost-kernel backend need

needs

> to receive IOTLB entry for used ring
> information early, which is done by triggering a miss event on
> its address.
> 
> This patch extends this behaviour to all rings information, to be
> compatible with vhost-user backend design.

Why does vhost-user need it though?

> 
> Signed-off-by: Maxime Coquelin <address@hidden>
> ---
> v2:
>  - Revert back to existing behaviour, i.e. only send IOTLB updates
> at ring enablement time, not at ring address setting time (mst).
>  - Extend IOTLB misses to all ring addresses, not only used ring.
> 
>  hw/virtio/vhost.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 6eddb09..7867034 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1552,11 +1552,15 @@ int vhost_dev_start(struct vhost_dev *hdev, 
> VirtIODevice *vdev)
>      if (vhost_dev_has_iommu(hdev)) {
>          hdev->vhost_ops->vhost_set_iotlb_callback(hdev, true);
>  
> -        /* Update used ring information for IOTLB to work correctly,
> -         * vhost-kernel code requires for this.*/
> +        /*
> +         * Update rings information for IOTLB to work correctly,
> +         * vhost-kernel and vhost-user codes require for this.

Better just say "Update ring info for vhost iotlb."

The rest isn't really informative.



> +         */
>          for (i = 0; i < hdev->nvqs; ++i) {
>              struct vhost_virtqueue *vq = hdev->vqs + i;
>              vhost_device_iotlb_miss(hdev, vq->used_phys, true);
> +            vhost_device_iotlb_miss(hdev, vq->desc_phys, true);
> +            vhost_device_iotlb_miss(hdev, vq->avail_phys, true);

So I don't remember why does vhost in kernel want miss on used
at start time.

Jason, could you comment on this please?



>          }
>      }
>      return 0;
> -- 
> 2.9.4