RE: [PATCH v5 17/19] vfio: Add VFIO_DEVICE_AT[DE]TACH_IOMMUFD_PT

Liu, Yi L
2023-02-28T12:42:38Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Tuesday, February 28, 2023 8:32 PM
>
> On Tue, Feb 28, 2023 at 02:51:28AM +0000, Liu, Yi L wrote:
> > > This seems strange. no iommu mode should have a NULL dev-
> >iommufctx.
> > > Why do we have a df->noiommu at all?
> >
> > This is due to the vfio_device_first_open(). Detail as below comment (part
> of
> > patch 0016).
> >
> > + /*
> > + * For group/container path, iommufd pointer is NULL when comes
> > + * into this helper. Its noiommu support is handled by
> > + * vfio_device_group_use_iommu()
> > + *
> > + * For iommufd compat mode, iommufd pointer here is a valid value.
> > + * Its noiommu support is in vfio_iommufd_bind().
> > + *
> > + * For device cdev path, iommufd pointer here is a valid value for
> > + * normal cases, but it is NULL if it's noiommu. Check df->noiommu
> > + * to differentiate cdev noiommu from the group/container path
> which
> > + * also passes NULL iommufd pointer in. If set then do nothing.
> > + */
>
> If the group is in iommufd mode then it should set this pointer too.

Yes, but the key point is that both the group in legacy mode and the
cdev path sets iommufd==NULL. And the handling for the two should
be different. So needs this extra info to differentiate them in
vfio_device_first_open().

Regards,
Yi Liu