Re: [PATCH 20/40] vdpa: avoid mapping flush across reset

[Jason Wang]

On Fri, Dec 8, 2023 at 2:52 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
> Leverage the IOTLB_PERSIST and DESC_ASID features to achieve
> a slightly light weight reset path, without resorting to
> suspend and resume. Not as best but it offers significant
> time saving too, which should somehow play its role in live
> migration down time reduction by large.
>
> It benefits two cases:
>   - normal virtio reset in the VM, e.g. guest reboot, don't
>     have to tear down all iotlb mapping and set up again.
>   - SVQ switching, in which data vq's descriptor table and
>     vrings are moved to a different ASID than where its
>     buffers reside. Along with the use of persistent iotlb,
>     it would save substantial time from pinning and mapping
>     unneccessarily when moving descriptors on to or out of
>     shadow mode.
>
> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>

Looks good to me.

Thanks

> ---
>  hw/virtio/vhost-vdpa.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 31e0a55..47c764b 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -633,6 +633,7 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void 
> *opaque, Error **errp)
>                                       0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH |
>                                       0x1ULL << VHOST_BACKEND_F_IOTLB_ASID |
>                                       0x1ULL << VHOST_BACKEND_F_DESC_ASID |
> +                                     0x1ULL << VHOST_BACKEND_F_IOTLB_PERSIST 
> |
>                                       0x1ULL << VHOST_BACKEND_F_SUSPEND;
>      int ret;
>
> @@ -1493,8 +1494,6 @@ static void vhost_vdpa_maybe_flush_map(struct vhost_dev 
> *dev)
>
>  static void vhost_vdpa_reset_status(struct vhost_dev *dev)
>  {
> -    struct vhost_vdpa *v = dev->opaque;
> -
>      if (!vhost_vdpa_last_dev(dev)) {
>          return;
>      }
> @@ -1502,9 +1501,7 @@ static void vhost_vdpa_reset_status(struct vhost_dev 
> *dev)
>      vhost_vdpa_reset_device(dev);
>      vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
>                                 VIRTIO_CONFIG_S_DRIVER);
> -    memory_listener_unregister(&v->shared->listener);
> -    v->shared->listener_registered = false;
> -
> +    vhost_vdpa_maybe_flush_map(dev);
>  }
>
>  static int vhost_vdpa_set_log_base(struct vhost_dev *dev, uint64_t base,
> --
> 1.8.3.1
>