Virtualization - Jan 2022 - [PATCH v7 03/14] vdpa: Sync calls set/get config/status with cf_mutex

On 1/9/2022 6:09 AM, Eli Cohen wrote:
> On Thu, Jan 06, 2022 at 04:33:49PM -0800, Si-Wei Liu wrote:
>>
>> On 1/5/2022 3:46 AM, Eli Cohen wrote:
>>> Add wrappers to get/set status and protect these operations with
>>> cf_mutex to serialize these operations with respect to get/set
config
>>> operations.
>>>
>>> Signed-off-by: Eli Cohen <elic at nvidia.com>
>>> ---
>>>    drivers/vdpa/vdpa.c          | 19 +++++++++++++++++++
>>>    drivers/vhost/vdpa.c         |  7 +++----
>>>    drivers/virtio/virtio_vdpa.c |  3 +--
>>>    include/linux/vdpa.h         |  3 +++
>>>    4 files changed, 26 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
>>> index 42d71d60d5dc..5134c83c4a22 100644
>>> --- a/drivers/vdpa/vdpa.c
>>> +++ b/drivers/vdpa/vdpa.c
>>> @@ -21,6 +21,25 @@ static LIST_HEAD(mdev_head);
>>>    static DEFINE_MUTEX(vdpa_dev_mutex);
>>>    static DEFINE_IDA(vdpa_index_ida);
>>> +u8 vdpa_get_status(struct vdpa_device *vdev)
>>> +{
>>> +	u8 status;
>>> +
>>> +	mutex_lock(&vdev->cf_mutex);
>>> +	status = vdev->config->get_status(vdev);
>>> +	mutex_unlock(&vdev->cf_mutex);
>>> +	return status;
>>> +}
>>> +EXPORT_SYMBOL(vdpa_get_status);
>>> +
>>> +void vdpa_set_status(struct vdpa_device *vdev, u8 status)
>>> +{
>>> +	mutex_lock(&vdev->cf_mutex);
>>> +	vdev->config->set_status(vdev, status);
>>> +	mutex_unlock(&vdev->cf_mutex);
>>> +}
>>> +EXPORT_SYMBOL(vdpa_set_status);
>>> +
>>>    static struct genl_family vdpa_nl_family;
>>>    static int vdpa_dev_probe(struct device *d)
>>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>>> index ebaa373e9b82..d9d499465e2e 100644
>>> --- a/drivers/vhost/vdpa.c
>>> +++ b/drivers/vhost/vdpa.c
>>> @@ -142,10 +142,9 @@ static long vhost_vdpa_get_device_id(struct
vhost_vdpa *v, u8 __user *argp)
>>>    static long vhost_vdpa_get_status(struct vhost_vdpa *v, u8
__user *statusp)
>>>    {
>>>    	struct vdpa_device *vdpa = v->vdpa;
>>> -	const struct vdpa_config_ops *ops = vdpa->config;
>>>    	u8 status;
>>> -	status = ops->get_status(vdpa);
>>> +	status = vdpa_get_status(vdpa);
>> Not sure why we need to take cf_mutex here. Appears to me only setters
>> (set_status and reset) need to take the lock in this function.
>>
> What if the implenentation of get_status() at the upstream driver
> requires some setup. Taking cf_mutex seems like a good thing to do.
This doesn't like vdpa_get_config() which doesn't need that kind of 
setup at all currently (though whether the legacy detection in 
vdpa_get_config is useful or not remains to be a pending question). Even 
if there's a need in future, we may add it once we get there, right?

It looks to me it's quite unlikely the cf_mutex is needed even in 
future, since the command line tool would never want to intervene 
internal virtio status via set_status() from the the netlink thread, 
while the guest driver is running and in control. It's doubtful this 
just serves no real purpose for foreseeable future, but just add 
unwarranted overhead unnecessarily.

Regards,
-Siwei


>
>>>    	if (copy_to_user(statusp, &status, sizeof(status)))
>>>    		return -EFAULT;
>>> @@ -164,7 +163,7 @@ static long vhost_vdpa_set_status(struct
vhost_vdpa *v, u8 __user *statusp)
>>>    	if (copy_from_user(&status, statusp, sizeof(status)))
>>>    		return -EFAULT;
>>> -	status_old = ops->get_status(vdpa);
>>> +	status_old = vdpa_get_status(vdpa);
>> Ditto.
>>
>>>    	/*
>>>    	 * Userspace shouldn't remove status bits unless reset the
>>> @@ -182,7 +181,7 @@ static long vhost_vdpa_set_status(struct
vhost_vdpa *v, u8 __user *statusp)
>>>    		if (ret)
>>>    			return ret;
>>>    	} else
>>> -		ops->set_status(vdpa, status);
>>> +		vdpa_set_status(vdpa, status);
>> The reset() call in the if branch above needs to take the cf_mutex, the
same
>> way as that for set_status(). The reset() is effectively
set_status(vdpa,
>> 0).
>>
> Right, I missed that. Will send a fix.
>
>> Thanks,
>> -Siwei
>>
>>>    	if ((status & VIRTIO_CONFIG_S_DRIVER_OK) &&
!(status_old & VIRTIO_CONFIG_S_DRIVER_OK))
>>>    		for (i = 0; i < nvqs; i++)
>>> diff --git a/drivers/virtio/virtio_vdpa.c
b/drivers/virtio/virtio_vdpa.c
>>> index a84b04ba3195..76504559bc25 100644
>>> --- a/drivers/virtio/virtio_vdpa.c
>>> +++ b/drivers/virtio/virtio_vdpa.c
>>> @@ -91,9 +91,8 @@ static u8 virtio_vdpa_get_status(struct
virtio_device *vdev)
>>>    static void virtio_vdpa_set_status(struct virtio_device *vdev,
u8 status)
>>>    {
>>>    	struct vdpa_device *vdpa = vd_get_vdpa(vdev);
>>> -	const struct vdpa_config_ops *ops = vdpa->config;
>>> -	return ops->set_status(vdpa, status);
>>> +	return vdpa_set_status(vdpa, status);
>>>    }
>>>    static void virtio_vdpa_reset(struct virtio_device *vdev)
>>> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
>>> index 9cc4291a79b3..ae047fae2603 100644
>>> --- a/include/linux/vdpa.h
>>> +++ b/include/linux/vdpa.h
>>> @@ -408,6 +408,9 @@ void vdpa_get_config(struct vdpa_device *vdev,
unsigned int offset,
>>>    		     void *buf, unsigned int len);
>>>    void vdpa_set_config(struct vdpa_device *dev, unsigned int
offset,
>>>    		     const void *buf, unsigned int length);
>>> +u8 vdpa_get_status(struct vdpa_device *vdev);
>>> +void vdpa_set_status(struct vdpa_device *vdev, u8 status);
>>> +
>>>    /**
>>>     * struct vdpa_mgmtdev_ops - vdpa device ops
>>>     * @dev_add: Add a vdpa device using alloc and register