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

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Message-ID: <3017552c-cf49-4357-8bc9-d47593024e29@oracle.com>
Date: Wed, 17 Jan 2024 15:30:50 -0500
From: Steven Sistare <steven.sistare@...cle.com>
To: Jason Wang <jasowang@...hat.com>,
        Mike Christie <michael.christie@...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 1/11/2024 9:28 PM, Jason Wang wrote:
> On Fri, Jan 12, 2024 at 12:18 AM Mike Christie
> <michael.christie@...cle.com> wrote:
>>
>> 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.

Very good, I will drop this patch.

- Steve