[PATCH 1/2] virtio: fix virtio_config_ops description

[PATCH 1/2] virtio: fix virtio_config_ops description

[Cornelia Huck]

- get_features has returned 64 bits since commit d025477368792
  ("virtio: add support for 64 bit features.")
- properly mark all optional callbacks

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---
 include/linux/virtio_config.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 32baf8e26735..7087ef946ba7 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -22,7 +22,7 @@ struct irq_affinity;
  *	offset: the offset of the configuration field
  *	buf: the buffer to read the field value from.
  *	len: the length of the buffer
- * @generation: config generation counter
+ * @generation: config generation counter (optional)
  *	vdev: the virtio_device
  *	Returns the config generation counter
  * @get_status: read the status byte
@@ -48,17 +48,17 @@ struct irq_affinity;
  * @del_vqs: free virtqueues found by find_vqs().
  * @get_features: get the array of feature bits for this device.
  *	vdev: the virtio_device
- *	Returns the first 32 feature bits (all we currently need).
+ *	Returns the first 64 feature bits (all we currently need).
  * @finalize_features: confirm what device features we'll be using.
  *	vdev: the virtio_device
  *	This gives the final feature bits for the device: it can change
  *	the dev->feature bits if it wants.
  *	Returns 0 on success or error status
- * @bus_name: return the bus name associated with the device
+ * @bus_name: return the bus name associated with the device (optional)
  *	vdev: the virtio_device
  *      This returns a pointer to the bus name a la pci_name from which
  *      the caller can then copy.
- * @set_vq_affinity: set the affinity for a virtqueue.
+ * @set_vq_affinity: set the affinity for a virtqueue (optional).
  * @get_vq_affinity: get the affinity for a virtqueue (optional).
  */
 typedef void vq_callback_t(struct virtqueue *);
-- 
2.17.2

[PATCH 2/2] virtio: document virtio_config_ops restrictions

[Cornelia Huck]

Some transports (e.g. virtio-ccw) implement virtio operations that
seem to be a simple read/write as something more involved that
cannot be done from an atomic context.

Give at least a hint about that.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---
 include/linux/virtio_config.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7087ef946ba7..987b6491b946 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -12,6 +12,11 @@ struct irq_affinity;
 
 /**
  * virtio_config_ops - operations for configuring a virtio device
+ * Note: Do not assume that a transport implements all of the operations
+ *       getting/setting a value as a simple read/write! Generally speaking,
+ *       any of @get/@set, @get_status/@set_status, or @get_features/
+ *       @finalize_features are NOT safe to be called from an atomic
+ *       context.
  * @get: read the value of a configuration field
  *	vdev: the virtio_device
  *	offset: the offset of the configuration field
-- 
2.17.2

Re: [PATCH 1/2] virtio: fix virtio_config_ops description

[Cornelia Huck]

On Thu,  3 Jan 2019 17:08:03 +0100
Cornelia Huck <cohuck@redhat.com> wrote:

> - get_features has returned 64 bits since commit d025477368792
>   ("virtio: add support for 64 bit features.")
> - properly mark all optional callbacks
> 
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  include/linux/virtio_config.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 32baf8e26735..7087ef946ba7 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -22,7 +22,7 @@ struct irq_affinity;
>   *	offset: the offset of the configuration field
>   *	buf: the buffer to read the field value from.
>   *	len: the length of the buffer
> - * @generation: config generation counter
> + * @generation: config generation counter (optional)
>   *	vdev: the virtio_device
>   *	Returns the config generation counter
>   * @get_status: read the status byte
> @@ -48,17 +48,17 @@ struct irq_affinity;
>   * @del_vqs: free virtqueues found by find_vqs().
>   * @get_features: get the array of feature bits for this device.
>   *	vdev: the virtio_device
> - *	Returns the first 32 feature bits (all we currently need).
> + *	Returns the first 64 feature bits (all we currently need).
>   * @finalize_features: confirm what device features we'll be using.
>   *	vdev: the virtio_device
>   *	This gives the final feature bits for the device: it can change
>   *	the dev->feature bits if it wants.
>   *	Returns 0 on success or error status
> - * @bus_name: return the bus name associated with the device
> + * @bus_name: return the bus name associated with the device (optional)
>   *	vdev: the virtio_device
>   *      This returns a pointer to the bus name a la pci_name from which
>   *      the caller can then copy.
> - * @set_vq_affinity: set the affinity for a virtqueue.
> + * @set_vq_affinity: set the affinity for a virtqueue (optional).
>   * @get_vq_affinity: get the affinity for a virtqueue (optional).
>   */
>  typedef void vq_callback_t(struct virtqueue *);

Ping. Any feedback on that patch?

Re: [PATCH 1/2] virtio: fix virtio_config_ops description

[Wei Wang]

On 01/14/2019 10:09 PM, Cornelia Huck wrote:
> On Thu,  3 Jan 2019 17:08:03 +0100
> Cornelia Huck <cohuck@redhat.com> wrote:
>
>> - get_features has returned 64 bits since commit d025477368792
>>    ("virtio: add support for 64 bit features.")
>> - properly mark all optional callbacks
>>
>> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
>> ---
>>   include/linux/virtio_config.h | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
>> index 32baf8e26735..7087ef946ba7 100644
>> --- a/include/linux/virtio_config.h
>> +++ b/include/linux/virtio_config.h
>> @@ -22,7 +22,7 @@ struct irq_affinity;
>>    *	offset: the offset of the configuration field
>>    *	buf: the buffer to read the field value from.
>>    *	len: the length of the buffer
>> - * @generation: config generation counter
>> + * @generation: config generation counter (optional)
>>    *	vdev: the virtio_device
>>    *	Returns the config generation counter
>>    * @get_status: read the status byte
>> @@ -48,17 +48,17 @@ struct irq_affinity;
>>    * @del_vqs: free virtqueues found by find_vqs().
>>    * @get_features: get the array of feature bits for this device.
>>    *	vdev: the virtio_device
>> - *	Returns the first 32 feature bits (all we currently need).
>> + *	Returns the first 64 feature bits (all we currently need).
>>    * @finalize_features: confirm what device features we'll be using.
>>    *	vdev: the virtio_device
>>    *	This gives the final feature bits for the device: it can change
>>    *	the dev->feature bits if it wants.
>>    *	Returns 0 on success or error status
>> - * @bus_name: return the bus name associated with the device
>> + * @bus_name: return the bus name associated with the device (optional)
>>    *	vdev: the virtio_device
>>    *      This returns a pointer to the bus name a la pci_name from which
>>    *      the caller can then copy.
>> - * @set_vq_affinity: set the affinity for a virtqueue.
>> + * @set_vq_affinity: set the affinity for a virtqueue (optional).
>>    * @get_vq_affinity: get the affinity for a virtqueue (optional).
>>    */
>>   typedef void vq_callback_t(struct virtqueue *);
> Ping. Any feedback on that patch?

Reviewed-by: Wei Wang <wei.w.wang@intel.com>

Best,
Wei

Re: [PATCH 1/2] virtio: fix virtio_config_ops description

[Michael S. Tsirkin]

On Tue, Jan 15, 2019 at 10:15:39AM +0800, Wei Wang wrote:
> On 01/14/2019 10:09 PM, Cornelia Huck wrote:
> > On Thu,  3 Jan 2019 17:08:03 +0100
> > Cornelia Huck <cohuck@redhat.com> wrote:
> > 
> > > - get_features has returned 64 bits since commit d025477368792
> > >    ("virtio: add support for 64 bit features.")
> > > - properly mark all optional callbacks
> > > 
> > > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > > ---
> > >   include/linux/virtio_config.h | 8 ++++----
> > >   1 file changed, 4 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > > index 32baf8e26735..7087ef946ba7 100644
> > > --- a/include/linux/virtio_config.h
> > > +++ b/include/linux/virtio_config.h
> > > @@ -22,7 +22,7 @@ struct irq_affinity;
> > >    *	offset: the offset of the configuration field
> > >    *	buf: the buffer to read the field value from.
> > >    *	len: the length of the buffer
> > > - * @generation: config generation counter
> > > + * @generation: config generation counter (optional)
> > >    *	vdev: the virtio_device
> > >    *	Returns the config generation counter
> > >    * @get_status: read the status byte
> > > @@ -48,17 +48,17 @@ struct irq_affinity;
> > >    * @del_vqs: free virtqueues found by find_vqs().
> > >    * @get_features: get the array of feature bits for this device.
> > >    *	vdev: the virtio_device
> > > - *	Returns the first 32 feature bits (all we currently need).
> > > + *	Returns the first 64 feature bits (all we currently need).
> > >    * @finalize_features: confirm what device features we'll be using.
> > >    *	vdev: the virtio_device
> > >    *	This gives the final feature bits for the device: it can change
> > >    *	the dev->feature bits if it wants.
> > >    *	Returns 0 on success or error status
> > > - * @bus_name: return the bus name associated with the device
> > > + * @bus_name: return the bus name associated with the device (optional)
> > >    *	vdev: the virtio_device
> > >    *      This returns a pointer to the bus name a la pci_name from which
> > >    *      the caller can then copy.
> > > - * @set_vq_affinity: set the affinity for a virtqueue.
> > > + * @set_vq_affinity: set the affinity for a virtqueue (optional).
> > >    * @get_vq_affinity: get the affinity for a virtqueue (optional).
> > >    */
> > >   typedef void vq_callback_t(struct virtqueue *);
> > Ping. Any feedback on that patch?
> 
> Reviewed-by: Wei Wang <wei.w.wang@intel.com>
> 
> Best,
> Wei

Pushed already, can't add tags.
Sorry about that.

-- 
MST

Re: [PATCH 2/2] virtio: document virtio_config_ops restrictions

[Michael S. Tsirkin]

On Thu, Jan 03, 2019 at 05:08:04PM +0100, Cornelia Huck wrote:
> Some transports (e.g. virtio-ccw) implement virtio operations that
> seem to be a simple read/write as something more involved that
> cannot be done from an atomic context.
> 
> Give at least a hint about that.
> 
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  include/linux/virtio_config.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 7087ef946ba7..987b6491b946 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -12,6 +12,11 @@ struct irq_affinity;
>  
>  /**
>   * virtio_config_ops - operations for configuring a virtio device
> + * Note: Do not assume that a transport implements all of the operations
> + *       getting/setting a value as a simple read/write! Generally speaking,
> + *       any of @get/@set, @get_status/@set_status, or @get_features/
> + *       @finalize_features are NOT safe to be called from an atomic
> + *       context.
>   * @get: read the value of a configuration field
>   *	vdev: the virtio_device
>   *	offset: the offset of the configuration field

Then might_sleep in virtio_cread/virtio_cwrite and
friends would be appropriate? I guess we'll need to fix
balloon first.

> -- 
> 2.17.2

Re: [PATCH 2/2] virtio: document virtio_config_ops restrictions

[Cornelia Huck]

On Thu, 3 Jan 2019 11:28:28 -0500
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Thu, Jan 03, 2019 at 05:08:04PM +0100, Cornelia Huck wrote:
> > Some transports (e.g. virtio-ccw) implement virtio operations that
> > seem to be a simple read/write as something more involved that
> > cannot be done from an atomic context.
> > 
> > Give at least a hint about that.
> > 
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> >  include/linux/virtio_config.h | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > index 7087ef946ba7..987b6491b946 100644
> > --- a/include/linux/virtio_config.h
> > +++ b/include/linux/virtio_config.h
> > @@ -12,6 +12,11 @@ struct irq_affinity;
> >  
> >  /**
> >   * virtio_config_ops - operations for configuring a virtio device
> > + * Note: Do not assume that a transport implements all of the operations
> > + *       getting/setting a value as a simple read/write! Generally speaking,
> > + *       any of @get/@set, @get_status/@set_status, or @get_features/
> > + *       @finalize_features are NOT safe to be called from an atomic
> > + *       context.
> >   * @get: read the value of a configuration field
> >   *	vdev: the virtio_device
> >   *	offset: the offset of the configuration field  
> 
> Then might_sleep in virtio_cread/virtio_cwrite and
> friends would be appropriate? I guess we'll need to fix
> balloon first.

Yes, it makes sense to go over the code and add might_sleep to
functions where it makes sense after the balloon changes have been
merged.

Re: [PATCH 2/2] virtio: document virtio_config_ops restrictions

[Cornelia Huck]

On Thu, 3 Jan 2019 18:28:49 +0100
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Thu,  3 Jan 2019 17:08:04 +0100
> Cornelia Huck <cohuck@redhat.com> wrote:
> 
> > Some transports (e.g. virtio-ccw) implement virtio operations that
> > seem to be a simple read/write as something more involved that
> > cannot be done from an atomic context.
> > 
> > Give at least a hint about that.
> > 
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> >  include/linux/virtio_config.h | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > index 7087ef946ba7..987b6491b946 100644
> > --- a/include/linux/virtio_config.h
> > +++ b/include/linux/virtio_config.h
> > @@ -12,6 +12,11 @@ struct irq_affinity;
> >  
> >  /**
> >   * virtio_config_ops - operations for configuring a virtio device
> > + * Note: Do not assume that a transport implements all of the operations
> > + *       getting/setting a value as a simple read/write! Generally speaking,
> > + *       any of @get/@set, @get_status/@set_status, or @get_features/
> > + *       @finalize_features are NOT safe to be called from an atomic
> > + *       context.  
> 
> I think the only exception is @bus_name (and maybe @generation, I don't
> know) because it does not have to 'speak' with the hypervisor. If a
> transport operation has to 'speak' with the hypervisor, we do it by
> making it interpret a channel program. That means not safe to be called
> form atomic context. Or am I missing something?

I explicitly singled out the listed callbacks because they read/write a
value and there might be more to them than meets the eye. I would
assume that nobody expects calling e.g. find_vqs (allocating queues)
from an atomic context to be a good idea :) Maybe I should do
s/Generally speaking/In particular/ ?

That said, it's only a hint; we should add might_sleep as well to
interfaces where it makes sense.

Re: [virtio-dev] [PATCH 2/2] virtio: document virtio_config_ops restrictions

[Wei Wang]

On 01/04/2019 12:08 AM, Cornelia Huck wrote:
> Some transports (e.g. virtio-ccw) implement virtio operations that
> seem to be a simple read/write as something more involved that
> cannot be done from an atomic context.
>
> Give at least a hint about that.
>
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
>   include/linux/virtio_config.h | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 7087ef946ba7..987b6491b946 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -12,6 +12,11 @@ struct irq_affinity;
>   
>   /**
>    * virtio_config_ops - operations for configuring a virtio device
> + * Note: Do not assume that a transport implements all of the operations
> + *       getting/setting a value as a simple read/write! Generally speaking,
> + *       any of @get/@set, @get_status/@set_status, or @get_features/
> + *       @finalize_features are NOT safe to be called from an atomic
> + *       context.
>    * @get: read the value of a configuration field
>    *	vdev: the virtio_device
>    *	offset: the offset of the configuration field


Reviewed-by: Wei Wang <wei.w.wang@intel.com>

Best,
Wei