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Subject: Re: [PATCH 2/3] vdpa/mlx5: Only return vq ready if vq is initialized
To:     Eli Cohen <elic@nvidia.com>
Cc:     mst@redhat.com, virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
References: <20210531160448.31537-1-elic@nvidia.com>
 <0fbd8484-9e8b-d7cc-4996-74306e6e2867@redhat.com>
 <20210601041351.GC203469@mtl-vdi-166.wap.labs.mlnx>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <67b26a20-b418-4893-a42f-f03852c2123e@redhat.com>
Date:   Tue, 1 Jun 2021 13:03:36 +0800
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在 2021/6/1 下午12:13, Eli Cohen 写道:
> On Tue, Jun 01, 2021 at 10:18:04AM +0800, Jason Wang wrote:
>> 在 2021/6/1 上午12:04, Eli Cohen 写道:
>>> Only return the value of the ready field if the VQ is initialized in
>>> which case the value of the field is valid.
>>>
>>> Failing to do so can result in virtio_vdpa failing to load if the device
>>> was previously used by vhost_vdpa and the old values are ready.
>>> virtio_vdpa expects to find VQs in "not ready" state.
>>>
>>> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
>>> Signed-off-by: Eli Cohen <elic@nvidia.com>
>>> ---
>>>    drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>> index 02a05492204c..f6b680d2ab1c 100644
>>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>> @@ -1407,7 +1407,7 @@ static bool mlx5_vdpa_get_vq_ready(struct vdpa_device *vdev, u16 idx)
>>>    	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
>>>    	struct mlx5_vdpa_virtqueue *mvq = &ndev->vqs[idx];
>>> -	return mvq->ready;
>>> +	return mvq->initialized && mvq->ready;
>>
>> I think the more suitable fix is to reset mvq->ready during reset. The
>> vq_ready should follow the queue_enable semantic in virtio-pci:
>>
>> "
>> The device MUST present a 0 in queue_enable on reset.
>> "
> Thinking again, I think we should call set_vq_ready() from
> qemu/virtio_vdpa etc. after reset to explicitly set ready to false.


This is not what I read from the spec and how the current driver behave.

And I don't see why we need to stick to 1 after the reset.


>
> The ready indication is not necessairily a reflection of the hardware
> queue:
>
> "Virtual queue ready bit
> Writing one (0x1) to this register notifies the device that it can
> execute requests from this virtual queue. Reading from this register
> returns the last value written to it. Both read and write accesses apply
> to the queue selected by writing to QueueSel."


My understanding that this applies if not reset in the middle. We can 
clarify this in the spec if needed.

Thanks


>
>
>> Thanks
>>
>>
>>>    }
>>>    static int mlx5_vdpa_set_vq_state(struct vdpa_device *vdev, u16 idx,