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Date: Mon, 8 Feb 2021 17:04:27 +0800
From: Jason Wang <jasowang@...hat.com>
To: Eli Cohen <elic@...dia.com>
Cc: Si-Wei Liu <si-wei.liu@...cle.com>, mst@...hat.com,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, lulu@...hat.com
Subject: Re: [PATCH v1] vdpa/mlx5: Restore the hardware used index after
change map
On 2021/2/8 下午2:37, Eli Cohen wrote:
> On Mon, Feb 08, 2021 at 12:27:18PM +0800, Jason Wang wrote:
>> On 2021/2/6 上午7:07, Si-Wei Liu wrote:
>>>
>>> On 2/3/2021 11:36 PM, Eli Cohen wrote:
>>>> When a change of memory map occurs, the hardware resources are destroyed
>>>> and then re-created again with the new memory map. In such case, we need
>>>> to restore the hardware available and used indices. The driver failed to
>>>> restore the used index which is added here.
>>>>
>>>> Also, since the driver also fails to reset the available and used
>>>> indices upon device reset, fix this here to avoid regression caused by
>>>> the fact that used index may not be zero upon device reset.
>>>>
>>>> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5
>>>> devices")
>>>> Signed-off-by: Eli Cohen <elic@...dia.com>
>>>> ---
>>>> v0 -> v1:
>>>> Clear indices upon device reset
>>>>
>>>> drivers/vdpa/mlx5/net/mlx5_vnet.c | 18 ++++++++++++++++++
>>>> 1 file changed, 18 insertions(+)
>>>>
>>>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>> b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>> index 88dde3455bfd..b5fe6d2ad22f 100644
>>>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>>> @@ -87,6 +87,7 @@ struct mlx5_vq_restore_info {
>>>> u64 device_addr;
>>>> u64 driver_addr;
>>>> u16 avail_index;
>>>> + u16 used_index;
>>>> bool ready;
>>>> struct vdpa_callback cb;
>>>> bool restore;
>>>> @@ -121,6 +122,7 @@ struct mlx5_vdpa_virtqueue {
>>>> u32 virtq_id;
>>>> struct mlx5_vdpa_net *ndev;
>>>> u16 avail_idx;
>>>> + u16 used_idx;
>>>> int fw_state;
>>>> /* keep last in the struct */
>>>> @@ -804,6 +806,7 @@ static int create_virtqueue(struct mlx5_vdpa_net
>>>> *ndev, struct mlx5_vdpa_virtque
>>>> obj_context = MLX5_ADDR_OF(create_virtio_net_q_in, in,
>>>> obj_context);
>>>> MLX5_SET(virtio_net_q_object, obj_context, hw_available_index,
>>>> mvq->avail_idx);
>>>> + MLX5_SET(virtio_net_q_object, obj_context, hw_used_index,
>>>> mvq->used_idx);
>>>> MLX5_SET(virtio_net_q_object, obj_context,
>>>> queue_feature_bit_mask_12_3,
>>>> get_features_12_3(ndev->mvdev.actual_features));
>>>> vq_ctx = MLX5_ADDR_OF(virtio_net_q_object, obj_context,
>>>> virtio_q_context);
>>>> @@ -1022,6 +1025,7 @@ static int connect_qps(struct mlx5_vdpa_net
>>>> *ndev, struct mlx5_vdpa_virtqueue *m
>>>> struct mlx5_virtq_attr {
>>>> u8 state;
>>>> u16 available_index;
>>>> + u16 used_index;
>>>> };
>>>> static int query_virtqueue(struct mlx5_vdpa_net *ndev, struct
>>>> mlx5_vdpa_virtqueue *mvq,
>>>> @@ -1052,6 +1056,7 @@ static int query_virtqueue(struct
>>>> mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueu
>>>> memset(attr, 0, sizeof(*attr));
>>>> attr->state = MLX5_GET(virtio_net_q_object, obj_context, state);
>>>> attr->available_index = MLX5_GET(virtio_net_q_object,
>>>> obj_context, hw_available_index);
>>>> + attr->used_index = MLX5_GET(virtio_net_q_object, obj_context,
>>>> hw_used_index);
>>>> kfree(out);
>>>> return 0;
>>>> @@ -1535,6 +1540,16 @@ static void teardown_virtqueues(struct
>>>> mlx5_vdpa_net *ndev)
>>>> }
>>>> }
>>>> +static void clear_virtqueues(struct mlx5_vdpa_net *ndev)
>>>> +{
>>>> + int i;
>>>> +
>>>> + for (i = ndev->mvdev.max_vqs - 1; i >= 0; i--) {
>>>> + ndev->vqs[i].avail_idx = 0;
>>>> + ndev->vqs[i].used_idx = 0;
>>>> + }
>>>> +}
>>>> +
>>>> /* TODO: cross-endian support */
>>>> static inline bool mlx5_vdpa_is_little_endian(struct mlx5_vdpa_dev
>>>> *mvdev)
>>>> {
>>>> @@ -1610,6 +1625,7 @@ static int save_channel_info(struct
>>>> mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqu
>>>> return err;
>>>> ri->avail_index = attr.available_index;
>>>> + ri->used_index = attr.used_index;
>>>> ri->ready = mvq->ready;
>>>> ri->num_ent = mvq->num_ent;
>>>> ri->desc_addr = mvq->desc_addr;
>>>> @@ -1654,6 +1670,7 @@ static void restore_channels_info(struct
>>>> mlx5_vdpa_net *ndev)
>>>> continue;
>>>> mvq->avail_idx = ri->avail_index;
>>>> + mvq->used_idx = ri->used_index;
>>>> mvq->ready = ri->ready;
>>>> mvq->num_ent = ri->num_ent;
>>>> mvq->desc_addr = ri->desc_addr;
>>>> @@ -1768,6 +1785,7 @@ static void mlx5_vdpa_set_status(struct
>>>> vdpa_device *vdev, u8 status)
>>>> if (!status) {
>>>> mlx5_vdpa_info(mvdev, "performing device reset\n");
>>>> teardown_driver(ndev);
>>>> + clear_virtqueues(ndev);
>>> The clearing looks fine at the first glance, as it aligns with the other
>>> state cleanups floating around at the same place. However, the thing is
>>> get_vq_state() is supposed to be called right after to get sync'ed with
>>> the latest internal avail_index from device while vq is stopped. The
>>> index was saved in the driver software at vq suspension, but before the
>>> virtq object is destroyed. We shouldn't clear the avail_index too early.
>>
>> Good point.
>>
>> There's a limitation on the virtio spec and vDPA framework that we can not
>> simply differ device suspending from device reset.
>>
> Are you talking about live migration where you reset the device but
> still want to know how far it progressed in order to continue from the
> same place in the new VM?
Yes. So if we want to support live migration at we need:
in src node:
1) suspend the device
2) get last_avail_idx via get_vq_state()
in the dst node:
3) set last_avail_idx via set_vq_state()
4) resume the device
So you can see, step 2 requires the device/driver not to forget the
last_avail_idx.
The annoying thing is that, in the virtio spec there's no definition of
device suspending. So we reuse set_status(0) right now for vq
suspending. Then if we forget last_avail_idx in set_status(0), it will
break the assumption of step 2).
>
>> Need to think about that. I suggest a new state in [1], the issue is that
>> people doesn't like the asynchronous API that it introduces.
>>
>>
>>> Possibly it can be postponed to where VIRTIO_CONFIG_S_DRIVER_OK gets set
>>> again, i.e. right before the setup_driver() in mlx5_vdpa_set_status()?
>>
>> Looks like a good workaround.
Rethink of this, this won't work for the step 4), if we reuse the
S_DRING_OK for resuming.
The most clean way is to invent the feature in virtio spec and implement
that in the driver.
Thanks
>>
>> Thanks
>>
>>
>>> -Siwei
>>
>> [1]
>> https://lists.oasis-open.org/archives/virtio-comment/202012/msg00029.html
>>
>>
>>>> mlx5_vdpa_destroy_mr(&ndev->mvdev);
>>>> ndev->mvdev.status = 0;
>>>> ndev->mvdev.mlx_features = 0;
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