Re: [PATCH 3/4] vdpa: get_iova_range() is mandatory for device specific DMA translation

[Jason Wang]

On 2020/8/5 下午8:55, Michael S. Tsirkin wrote:
> On Wed, Jun 17, 2020 at 11:29:46AM +0800, Jason Wang wrote:
> > In order to let userspace work correctly, get_iova_range() is a must
> > for the device that has its own DMA translation logic.
> I guess you mean for a device.
>
> However in absence of ths op, I don't see what is wrong with just
> assuming device can access any address.


It's just for safe, if you want, we can assume any address without this op.


> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> >   drivers/vdpa/vdpa.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> > index de211ef3738c..ab7af978ef70 100644
> > --- a/drivers/vdpa/vdpa.c
> > +++ b/drivers/vdpa/vdpa.c
> > @@ -82,6 +82,10 @@ struct vdpa_device *__vdpa_alloc_device(struct device *parent,
> >   	if (!!config->dma_map != !!config->dma_unmap)
> >   		goto err;
> >   
> > +	if ((config->dma_map || config->set_map) &&
> > +	    !config->get_iova_range)
> > +		goto err;
> > +
> >   	err = -ENOMEM;
> >   	vdev = kzalloc(size, GFP_KERNEL);
> >   	if (!vdev)
> What about devices using an IOMMU for translation?
> IOMMUs generally have a limited IOVA range too, right?


See patch 4 which query the IOMMU geometry in this case:

+        iommu_domain_get_attr(v->domain,
+                      DOMAIN_ATTR_GEOMETRY, &geo);
+        range.start = geo.aperture_start;
+        range.end = geo.aperture_end;

Thanks


> > --
> > 2.20.1