netdev - Re: [PATCH 1/2] vdpa/mlx5: Fix suspend/resume index restoration

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Date:   Wed, 17 Feb 2021 13:51:12 -0800
From:   Si-Wei Liu <si-wei.liu@...cle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Eli Cohen <elic@...dia.com>, jasowang@...hat.com,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] vdpa/mlx5: Fix suspend/resume index restoration



On 2/17/2021 1:20 PM, Michael S. Tsirkin wrote:
> On Wed, Feb 17, 2021 at 11:42:48AM -0800, Si-Wei Liu wrote:
>>
>> On 2/16/2021 8:20 AM, Eli Cohen wrote:
>>> When we suspend the VM, the VDPA interface will be reset. When the VM is
>>> resumed again, clear_virtqueues() will clear the available and used
>>> indices resulting in hardware virqtqueue objects becoming out of sync.
>>> We can avoid this function alltogether since qemu will clear them if
>>> required, e.g. when the VM went through a reboot.
>>>
>>> Moreover, since the hw available and used indices should always be
>>> identical on query and should be restored to the same value same value
>>> for virtqueues that complete in order, we set the single value provided
>>> by set_vq_state(). In get_vq_state() we return the value of hardware
>>> used index.
>>>
>>> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
>>> Signed-off-by: Eli Cohen <elic@...dia.com>
>> Acked-by: Si-Wei Liu <si-wei.liu@...cle.com>
>
> Seems to also fix b35ccebe3ef76168aa2edaa35809c0232cb3578e, right?
I think so. It should have both "Fixes" tags.

-Siwei
>
>>> ---
>>>    drivers/vdpa/mlx5/net/mlx5_vnet.c | 17 ++++-------------
>>>    1 file changed, 4 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>> index b8e9d525d66c..a51b0f86afe2 100644
>>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>>> @@ -1169,6 +1169,7 @@ static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
>>>    		return;
>>>    	}
>>>    	mvq->avail_idx = attr.available_index;
>>> +	mvq->used_idx = attr.used_index;
>>>    }
>>>    static void suspend_vqs(struct mlx5_vdpa_net *ndev)
>>> @@ -1426,6 +1427,7 @@ static int mlx5_vdpa_set_vq_state(struct vdpa_device *vdev, u16 idx,
>>>    		return -EINVAL;
>>>    	}
>>> +	mvq->used_idx = state->avail_index;
>>>    	mvq->avail_idx = state->avail_index;
>>>    	return 0;
>>>    }
>>> @@ -1443,7 +1445,7 @@ static int mlx5_vdpa_get_vq_state(struct vdpa_device *vdev, u16 idx, struct vdpa
>>>    	 * that cares about emulating the index after vq is stopped.
>>>    	 */
>>>    	if (!mvq->initialized) {
>>> -		state->avail_index = mvq->avail_idx;
>>> +		state->avail_index = mvq->used_idx;
>>>    		return 0;
>>>    	}
>>> @@ -1452,7 +1454,7 @@ static int mlx5_vdpa_get_vq_state(struct vdpa_device *vdev, u16 idx, struct vdpa
>>>    		mlx5_vdpa_warn(mvdev, "failed to query virtqueue\n");
>>>    		return err;
>>>    	}
>>> -	state->avail_index = attr.available_index;
>>> +	state->avail_index = attr.used_index;
>>>    	return 0;
>>>    }
>>> @@ -1532,16 +1534,6 @@ 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)
>>>    {
>>> @@ -1777,7 +1769,6 @@ 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);
>>>    		mlx5_vdpa_destroy_mr(&ndev->mvdev);
>>>    		ndev->mvdev.status = 0;
>>>    		++mvdev->generation;