linux-kernel - Re: [RFC V1 07/13] vhost-vdpa: flush workers on suspend

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Date: Thu, 11 Jan 2024 10:17:58 -0600
From: Mike Christie <michael.christie@...cle.com>
To: Jason Wang <jasowang@...hat.com>,
        Steve Sistare <steven.sistare@...cle.com>
Cc: virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        Eugenio Perez Martin <eperezma@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Dragos Tatulea
 <dtatulea@...dia.com>, Eli Cohen <elic@...dia.com>,
        Xie Yongji <xieyongji@...edance.com>
Subject: Re: [RFC V1 07/13] vhost-vdpa: flush workers on suspend

On 1/10/24 9:09 PM, Jason Wang wrote:
> On Thu, Jan 11, 2024 at 4:40 AM Steve Sistare <steven.sistare@...cle.com> wrote:
>>
>> To pass ownership of a live vdpa device to a new process, the user
>> suspends the device, calls VHOST_NEW_OWNER to change the mm, and calls
>> VHOST_IOTLB_REMAP to change the user virtual addresses to match the new
>> mm.  Flush workers in suspend to guarantee that no worker sees the new
>> mm and old VA in between.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
>> ---
>>  drivers/vhost/vdpa.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>> index 8fe1562d24af..9673e8e20d11 100644
>> --- a/drivers/vhost/vdpa.c
>> +++ b/drivers/vhost/vdpa.c
>> @@ -591,10 +591,14 @@ static long vhost_vdpa_suspend(struct vhost_vdpa *v)
>>  {
>>         struct vdpa_device *vdpa = v->vdpa;
>>         const struct vdpa_config_ops *ops = vdpa->config;
>> +       struct vhost_dev *vdev = &v->vdev;
>>
>>         if (!ops->suspend)
>>                 return -EOPNOTSUPP;
>>
>> +       if (vdev->use_worker)
>> +               vhost_dev_flush(vdev);
> 
> It looks to me like it's better to check use_woker in vhost_dev_flush.
> 

You can now just call vhost_dev_flush and it will do the right thing.
The xa_for_each loop will only flush workers if they have been setup,
so for vdpa it will not find/flush anything.