vhost_vdpa: no need to fetch vring base when poweroff

In the poweroff routine, no need to fetch last available index.

This commit also provides a better debug message in the vhost
caller vhost_virtqueue_stop, because if vhost does not fetch
the last avail idx successfully, maybe the device does not
suspend, vhost will sync last avail idx to vring used idx as a
work around, not a failure.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
---
 hw/virtio/vhost-vdpa.c | 4 ++++
 hw/virtio/vhost.c      | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

On Fri, Jul 7, 2023 at 12:18 PM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
>
> In the poweroff routine, no need to fetch last available index.
>
> This commit also provides a better debug message in the vhost
> caller vhost_virtqueue_stop, because if vhost does not fetch
> the last avail idx successfully, maybe the device does not
> suspend, vhost will sync last avail idx to vring used idx as a
> work around, not a failure.
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>

CCing MST.

> ---
>  hw/virtio/vhost-vdpa.c | 4 ++++
>  hw/virtio/vhost.c      | 2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 3c575a9a6e..f62952e1c7 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -26,6 +26,7 @@
>  #include "cpu.h"
>  #include "trace.h"
>  #include "qapi/error.h"
> +#include "sysemu/runstate.h"
>
>  /*
>   * Return one past the end of the end of section. Be careful with uint64_t
> @@ -1391,6 +1392,9 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
>      struct vhost_vdpa *v = dev->opaque;
>      int ret;
>
> +    if (runstate_check(RUN_STATE_SHUTDOWN))
> +        return 0;
> +

QEMU coding style mandates braces around the "if" body (CODING_STYLE.rst file).

Apart from that I think we should add a comment here. Something in the line of:

Some devices do not support the call properly, and we don't need to
retrieve the indexes if we're not migrating. Skip it in this case.

>      if (v->shadow_vqs_enabled) {
>          ring->num = virtio_queue_get_last_avail_idx(dev->vdev, ring->index);
>          return 0;
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 82394331bf..84712743e0 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1262,7 +1262,7 @@ void vhost_virtqueue_stop(struct vhost_dev *dev,
>
>      r = dev->vhost_ops->vhost_get_vring_base(dev, &state);
>      if (r < 0) {
> -        VHOST_OPS_DEBUG(r, "vhost VQ %u ring restore failed: %d", idx, r);
> +        VHOST_OPS_DEBUG(r, "sync last avail idx to the used idx for vhost VQ %u", idx);

Guest's used idx? Also, maybe it is worth splitting this in a separated patch.

Apart from the nitpicking, I think the general line of the patch is
the way to go :).

Thanks!

>          /* Connection to the backend is broken, so let's sync internal
>           * last avail idx to the device used idx.
>           */
> --
> 2.39.3
>

On 7/7/2023 7:02 PM, Eugenio Perez Martin wrote:
> On Fri, Jul 7, 2023 at 12:18 PM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
>> In the poweroff routine, no need to fetch last available index.
>>
>> This commit also provides a better debug message in the vhost
>> caller vhost_virtqueue_stop, because if vhost does not fetch
>> the last avail idx successfully, maybe the device does not
>> suspend, vhost will sync last avail idx to vring used idx as a
>> work around, not a failure.
>>
>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> CCing MST.
>
>> ---
>>   hw/virtio/vhost-vdpa.c | 4 ++++
>>   hw/virtio/vhost.c      | 2 +-
>>   2 files changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
>> index 3c575a9a6e..f62952e1c7 100644
>> --- a/hw/virtio/vhost-vdpa.c
>> +++ b/hw/virtio/vhost-vdpa.c
>> @@ -26,6 +26,7 @@
>>   #include "cpu.h"
>>   #include "trace.h"
>>   #include "qapi/error.h"
>> +#include "sysemu/runstate.h"
>>
>>   /*
>>    * Return one past the end of the end of section. Be careful with uint64_t
>> @@ -1391,6 +1392,9 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
>>       struct vhost_vdpa *v = dev->opaque;
>>       int ret;
>>
>> +    if (runstate_check(RUN_STATE_SHUTDOWN))
>> +        return 0;
>> +
> QEMU coding style mandates braces around the "if" body (CODING_STYLE.rst file).
>
> Apart from that I think we should add a comment here. Something in the line of:
>
> Some devices do not support the call properly, and we don't need to
> retrieve the indexes if we're not migrating. Skip it in this case.
V2 will include these changes, thanks!
>
>>       if (v->shadow_vqs_enabled) {
>>           ring->num = virtio_queue_get_last_avail_idx(dev->vdev, ring->index);
>>           return 0;
>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>> index 82394331bf..84712743e0 100644
>> --- a/hw/virtio/vhost.c
>> +++ b/hw/virtio/vhost.c
>> @@ -1262,7 +1262,7 @@ void vhost_virtqueue_stop(struct vhost_dev *dev,
>>
>>       r = dev->vhost_ops->vhost_get_vring_base(dev, &state);
>>       if (r < 0) {
>> -        VHOST_OPS_DEBUG(r, "vhost VQ %u ring restore failed: %d", idx, r);
>> +        VHOST_OPS_DEBUG(r, "sync last avail idx to the used idx for vhost VQ %u", idx);
> Guest's used idx? Also, maybe it is worth splitting this in a separated patch.
Yes, guest used idx is much clearer. I am not sure whether this worthy a 
separated
patch, this is only a comment.
>
> Apart from the nitpicking, I think the general line of the patch is
> the way to go :).
Thanks!
>
> Thanks!
>
>>           /* Connection to the backend is broken, so let's sync internal
>>            * last avail idx to the device used idx.
>>            */
>> --
>> 2.39.3
>>