RE: [PATCH v5 16/19] vfio: Add VFIO_DEVICE_BIND_IOMMUFD

Liu, Yi L
2023-03-03T06:57:39Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Thursday, March 2, 2023 1:47 AM
>
> On Wed, Mar 01, 2023 at 09:19:07AM +0000, Liu, Yi L wrote:
> > > From: Liu, Yi L <yi.l.liu@intel.com>
> > > Sent: Monday, February 27, 2023 7:12 PM
> > [...]
> > > +long vfio_device_ioctl_bind_iommufd(struct vfio_device_file *df,
> > > + unsigned long arg)
> > > +{
> > > + struct vfio_device *device = df->device;
> > > + struct vfio_device_bind_iommufd bind;
> > > + struct iommufd_ctx *iommufd = NULL;
> > > + unsigned long minsz;
> > > + int ret;
> > > +
> > > + minsz = offsetofend(struct vfio_device_bind_iommufd, out_devid);
> > > +
> > > + if (copy_from_user(&bind, (void __user *)arg, minsz))
> > > + return -EFAULT;
> > > +
> > > + if (bind.argsz < minsz || bind.flags)
> > > + return -EINVAL;
> > > +
> > > + if (!device->ops->bind_iommufd)
> > > + return -ENODEV;
> >
> > Hi Jason,
> >
> > Per the comment in vfio_iommufd_bind(), such device driver
> > won't provide .bind_iommufd(). So shall we allow this ioctl
> > to go longer to call .open_device() instead of failing it here?
> > I think we need to allow it to go further. E.g. leave the check
> > to be in vfio_iommufd_bind(). Otherwise, user may not able
> > to use such devices. Is it?
>
> You are thinking about the crazy mdev samples?
>
> We should probably just change them to provide a 'no dma' set of ops.
>
> > > +struct vfio_device_bind_iommufd {
> > > + __u32 argsz;
> > > + __u32 flags;
> > > + __aligned_u64 dev_cookie;
> > > + __s32 iommufd;
> > > + __u32 out_devid;
> >
> > As above, for the devices that do not do DMA, there is no .bind_iommufd
> > op, hence no iommufd_device generated. This means no good value
> > can be filled in this out_devid field. So this field is optional. Only
> > for the devices which do DMA, should this out_devid field return a
> > valid ID otherwise an invalid ID would be filled (e.g. value #0 is an
> > invalid value in the iommufd object id pool). Userspace needs to
> > check if the out_devid is valid or not before use. This ID can be further
> > used in iommufd uAPIs like IOMMU_HWPT_ALLOC,
> IOMMU_DEVICE_GET_INFO
> > and etc.
>
> I would say create an access and harmonize the no-DMA devices with the
> emulated devices.

How about below change?

diff --git a/drivers/vfio/iommufd.c b/drivers/vfio/iommufd.c
index 4f82a6fa7c6c..e536515086d7 100644
--- a/drivers/vfio/iommufd.c
+++ b/drivers/vfio/iommufd.c
@@ -18,12 +18,8 @@ int vfio_iommufd_bind(struct vfio_device *vdev, struct iommufd_ctx *ictx)

lockdep_assert_held(&vdev->dev_set->lock);

- /*
- * If the driver doesn't provide this op then it means the device does
- * not do DMA at all. So nothing to do.
- */
- if (!vdev->ops->bind_iommufd)
- return 0;
+ if (WARN_ON(!vdev->ops->bind_iommufd))
+ return -ENODEV;

ret = vdev->ops->bind_iommufd(vdev, ictx, &device_id);
if (ret)
@@ -102,7 +98,9 @@ EXPORT_SYMBOL_GPL(vfio_iommufd_physical_attach_ioas);
/*
* The emulated standard ops mean that vfio_device is going to use the
* "mdev path" and will call vfio_pin_pages()/vfio_dma_rw(). Drivers using this
- * ops set should call vfio_register_emulated_iommu_dev().
+ * ops set should call vfio_register_emulated_iommu_dev(). Drivers that do
+ * not call vfio_pin_pages()/vfio_dma_rw() has no need to provide dma_unmap
+ * callback.
*/

static void vfio_emulated_unmap(void *data, unsigned long iova,
@@ -110,7 +107,8 @@ static void vfio_emulated_unmap(void *data, unsigned long iova,
{
struct vfio_device *vdev = data;

- vdev->ops->dma_unmap(vdev, iova, length);
+ if (vdev->ops->dma_unmap)
+ vdev->ops->dma_unmap(vdev, iova, length);
}

static const struct iommufd_access_ops vfio_user_ops = {
diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
index e54eb752e1ba..19391dda5fba 100644
--- a/samples/vfio-mdev/mbochs.c
+++ b/samples/vfio-mdev/mbochs.c
@@ -1374,6 +1374,9 @@ static const struct vfio_device_ops mbochs_dev_ops = {
.write = mbochs_write,
.ioctl = mbochs_ioctl,
.mmap = mbochs_mmap,
+ .bind_iommufd = vfio_iommufd_emulated_bind,
+ .unbind_iommufd = vfio_iommufd_emulated_unbind,
+ .attach_ioas = vfio_iommufd_emulated_attach_ioas,
};

static struct mdev_driver mbochs_driver = {
diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c
index e8400fdab71d..5f48aef36995 100644
--- a/samples/vfio-mdev/mdpy.c
+++ b/samples/vfio-mdev/mdpy.c
@@ -663,6 +663,9 @@ static const struct vfio_device_ops mdpy_dev_ops = {
.write = mdpy_write,
.ioctl = mdpy_ioctl,
.mmap = mdpy_mmap,
+ .bind_iommufd = vfio_iommufd_emulated_bind,
+ .unbind_iommufd = vfio_iommufd_emulated_unbind,
+ .attach_ioas = vfio_iommufd_emulated_attach_ioas,
};

static struct mdev_driver mdpy_driver = {
diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
index e887de672c52..35460901b9f7 100644
--- a/samples/vfio-mdev/mtty.c
+++ b/samples/vfio-mdev/mtty.c
@@ -1269,6 +1269,9 @@ static const struct vfio_device_ops mtty_dev_ops = {
.read = mtty_read,
.write = mtty_write,
.ioctl = mtty_ioctl,
+ .bind_iommufd = vfio_iommufd_emulated_bind,
+ .unbind_iommufd = vfio_iommufd_emulated_unbind,
+ .attach_ioas = vfio_iommufd_emulated_attach_ioas,
};

static struct mdev_driver mtty_driver = {

> What should we return here anyhow if an access was created?

iommufd_access->obj.id. should be fine. Is it?

Regards,
Yi Liu