Re: [PATCH 2/2] vDPA/ifcvf: implement doorbell mapping for ifcvf

[Zhu, Lingshan]

On 4/28/2021 4:42 PM, Jason Wang wrote:
> 在 2021/4/28 下午4:21, Zhu Lingshan 写道:
> > This commit implements doorbell mapping feature for ifcvf.
> > This feature maps the notify page to userspace, to eliminate
> > vmexit when kick a vq.
> >
> > Signed-off-by: Zhu Lingshan <lingshan.zhu@xxxxxxxxx>
> > ---
> >   drivers/vdpa/ifcvf/ifcvf_main.c | 18 ++++++++++++++++++
> >   1 file changed, 18 insertions(+)
> >
> > diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c 
> > b/drivers/vdpa/ifcvf/ifcvf_main.c
> > index e48e6b74fe2e..afcb71bc0f51 100644
> > --- a/drivers/vdpa/ifcvf/ifcvf_main.c
> > +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
> > @@ -413,6 +413,23 @@ static int ifcvf_vdpa_get_vq_irq(struct 
> > vdpa_device *vdpa_dev,
> >       return vf->vring[qid].irq;
> >   }
> >   +static struct vdpa_notification_area 
> > ifcvf_get_vq_notification(struct vdpa_device *vdpa_dev,
> > +                                   u16 idx)
> > +{
> > +    struct ifcvf_hw *vf = vdpa_to_vf(vdpa_dev);
> > +    struct vdpa_notification_area area;
> > +
> > +    if (vf->notify_pa % PAGE_SIZE) {
> > +        area.addr = 0;
> > +        area.size = 0;
>
>
> We don't need this since:
>
> 1) there's a check in the vhost vDPA
I think you mean this code block in vdpa.c
        notify = ops->get_vq_notification(vdpa, index);
        if (notify.addr & (PAGE_SIZE - 1))
                return -EINVAL;

This should work, however, I think the parent driver should ensure it 
passes a PAGE_SIZE aligned address to userspace, to be robust, to be 
reliable.
> 2) device is unaware of the bound driver, non page aligned doorbell 
> doesn't necessarily meant it can be used
Yes, non page aligned doorbell can not be used, so there is a check.

Thanks
Zhu Lingshan
> Let's leave those polices to the driver.
>
> Thanks
>
>
> > +    } else {
> > +        area.addr = vf->notify_pa;
> > +        area.size = PAGE_SIZE;
> > +    }
> > +
> > +    return area;
> > +}
> > +
> >   /*
> >    * IFCVF currently does't have on-chip IOMMU, so not
> >    * implemented set_map()/dma_map()/dma_unmap()
> > @@ -440,6 +457,7 @@ static const struct vdpa_config_ops ifc_vdpa_ops = {
> >       .get_config    = ifcvf_vdpa_get_config,
> >       .set_config    = ifcvf_vdpa_set_config,
> >       .set_config_cb  = ifcvf_vdpa_set_config_cb,
> > +    .get_vq_notification = ifcvf_get_vq_notification,
> >   };
> >     static int ifcvf_probe(struct pci_dev *pdev, const struct 
> > pci_device_id *id)