linux-kernel - Re: [PATCH V1] vdpa: suspend and resume require DRIVER

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Date: Mon, 12 Feb 2024 09:56:31 -0500
From: Steven Sistare <steven.sistare@...cle.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>, Si-Wei Liu <si-wei.liu@...cle.com>,
        Eugenio Perez Martin <eperezma@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH V1] vdpa: suspend and resume require DRIVER_OK

On 2/12/2024 3:19 AM, Michael S. Tsirkin wrote:
> On Fri, Feb 09, 2024 at 02:29:59PM -0800, Steve Sistare wrote:
>> Calling suspend or resume requires VIRTIO_CONFIG_S_DRIVER_OK, for all
>> vdpa devices.
>>
>> Suggested-by: Eugenio Perez Martin <eperezma@...hat.com>"
>> Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
> 
> I don't think failing suspend or resume makes sense though -
> e.g. practically failing suspend will just prevent sleeping I think -
> why should guest not having driver loaded prevent system suspend?

Got it, my fix is too heavy handed.

> there's also state such as features set which does need to be
> preserved.
> 
> I think the thing to do is to skip invoking suspend/resume callback

OK.

>  and in
> fact checking suspend/resume altogether.

Currently ops->suspend, vhost_vdpa_can_suspend(), and VHOST_BACKEND_F_SUSPEND
are equivalent.  Hence if !ops->suspend, then then the driver does not support
it, and indeed may break if suspend is used, so system suspend must be blocked,
AFAICT.  Yielding:

    vhost_vdpa_suspend()
        if (!ops->suspend)
            return -EOPNOTSUPP;

        if (!(ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK))
            return 0;

- Steve

>> ---
>>  drivers/vhost/vdpa.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>> index bc4a51e4638b..ce1882acfc3b 100644
>> --- a/drivers/vhost/vdpa.c
>> +++ b/drivers/vhost/vdpa.c
>> @@ -598,6 +598,9 @@ static long vhost_vdpa_suspend(struct vhost_vdpa *v)
>>  	if (!ops->suspend)
>>  		return -EOPNOTSUPP;
>>  
>> +	if (!(ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK))
>> +		return -EINVAL;
>> +
>>  	ret = ops->suspend(vdpa);
>>  	if (!ret)
>>  		v->suspended = true;
>> @@ -618,6 +621,9 @@ static long vhost_vdpa_resume(struct vhost_vdpa *v)
>>  	if (!ops->resume)
>>  		return -EOPNOTSUPP;
>>  
>> +	if (!(ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK))
>> +		return -EINVAL;
>> +
>>  	ret = ops->resume(vdpa);
>>  	if (!ret)
>>  		v->suspended = false;
>> -- 
>> 2.39.3
>