linux-kernel - Re: [PATCH v2 19/24] vdpa: make sure set

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Date:   Wed, 5 Aug 2020 07:40:15 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 19/24] vdpa: make sure set_features in invoked for
 legacy

On Wed, Aug 05, 2020 at 02:14:07PM +0800, Jason Wang wrote:
> 
> On 2020/8/4 上午5:00, Michael S. Tsirkin wrote:
> > Some legacy guests just assume features are 0 after reset.
> > We detect that config space is accessed before features are
> > set and set features to 0 automatically.
> > Note: some legacy guests might not even access config space, if this is
> > reported in the field we might need to catch a kick to handle these.
> 
> 
> I wonder whether it's easier to just support modern device?
> 
> Thanks


Well hardware vendors are I think interested in supporting legacy
guests. Limiting vdpa to modern only would make it uncompetitive.



> 
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> >   drivers/vdpa/vdpa.c  |  1 +
> >   include/linux/vdpa.h | 34 ++++++++++++++++++++++++++++++++++
> >   2 files changed, 35 insertions(+)
> > 
> > diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> > index de211ef3738c..7105265e4793 100644
> > --- a/drivers/vdpa/vdpa.c
> > +++ b/drivers/vdpa/vdpa.c
> > @@ -96,6 +96,7 @@ struct vdpa_device *__vdpa_alloc_device(struct device *parent,
> >   	vdev->dev.release = vdpa_release_dev;
> >   	vdev->index = err;
> >   	vdev->config = config;
> > +	vdev->features_valid = false;
> >   	err = dev_set_name(&vdev->dev, "vdpa%u", vdev->index);
> >   	if (err)
> > diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> > index 239db794357c..29b8296f1414 100644
> > --- a/include/linux/vdpa.h
> > +++ b/include/linux/vdpa.h
> > @@ -33,12 +33,14 @@ struct vdpa_notification_area {
> >    * @dma_dev: the actual device that is performing DMA
> >    * @config: the configuration ops for this device.
> >    * @index: device index
> > + * @features_valid: were features initialized? for legacy guests
> >    */
> >   struct vdpa_device {
> >   	struct device dev;
> >   	struct device *dma_dev;
> >   	const struct vdpa_config_ops *config;
> >   	unsigned int index;
> > +	bool features_valid;
> >   };
> >   /**
> > @@ -266,4 +268,36 @@ static inline struct device *vdpa_get_dma_dev(struct vdpa_device *vdev)
> >   {
> >   	return vdev->dma_dev;
> >   }
> > +
> > +static inline void vdpa_reset(struct vdpa_device *vdev)
> > +{
> > +        const struct vdpa_config_ops *ops = vdev->config;
> > +
> > +	vdev->features_valid = false;
> > +        ops->set_status(vdev, 0);
> > +}
> > +
> > +static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features)
> > +{
> > +        const struct vdpa_config_ops *ops = vdev->config;
> > +
> > +	vdev->features_valid = true;
> > +        return ops->set_features(vdev, features);
> > +}
> > +
> > +
> > +static inline void vdpa_get_config(struct vdpa_device *vdev, unsigned offset,
> > +				   void *buf, unsigned int len)
> > +{
> > +        const struct vdpa_config_ops *ops = vdev->config;
> > +
> > +	/*
> > +	 * Config accesses aren't supposed to trigger before features are set.
> > +	 * If it does happen we assume a legacy guest.
> > +	 */
> > +	if (!vdev->features_valid)
> > +		vdpa_set_features(vdev, 0);
> > +	ops->get_config(vdev, offset, buf, len);
> > +}
> > +
> >   #endif /* _LINUX_VDPA_H */