RE: [PATCH v5 15/19] iommufd: vfio container FD ioctl compatibility

Tian, Kevin
2022-11-24T05:23:41Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, November 23, 2022 9:03 PM
>
> On Wed, Nov 23, 2022 at 01:33:22AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > Sent: Friday, November 18, 2022 11:22 PM
> > >
> > > On Fri, Nov 18, 2022 at 02:58:49AM +0000, Tian, Kevin wrote:
> > > > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > > > Sent: Thursday, November 17, 2022 5:01 AM
> > > > > index ca28a135b9675f..2fdff04000b326 100644
> > > > > --- a/drivers/iommu/iommufd/Makefile
> > > > > +++ b/drivers/iommu/iommufd/Makefile
> > > > > @@ -5,6 +5,7 @@ iommufd-y := \
> > > > > io_pagetable.o \
> > > > > ioas.o \
> > > > > main.o \
> > > > > - pages.o
> > > > > + pages.o \
> > > > > + vfio_compat.o
> > > > >
> > > >
> > > > move vfio_compat out of core? it's not required if VFIO
> > > > is not configured.
> > >
> > > We can, but I don't know if we should. Compat ioctls are part of
> > > /dev/iommu, and technically have nothing to do with VFIO. A native
> > > iommufd application using VDPA could use them, if it wanted, for
> > > instance.
> > >
> >
> > I'm not sure whether that requires further VDPA support. Be safe
> > I'd like VDPA to explicitly select vfio_compact when that new
> > mixed scheme is supported.
>
> It doesn't make any sense. The ioctls provided by the "vfio container"
> FD are entirely up to IOMMUFD, it doesn't matter what the consuming
> subsystem is. Just think of them as alternatives to the existing
> map/unmap iommfd provides in its native mode.
>
> If you want to disable them is a decision that is driven more by
> eliminating the code from the kernel because you know your userspace
> doesn't use those ioctls - which has nothing to do if vfio is compiled
> in or not.

if this can be compiled out then there is a dependency imposed by
vfio when vfio container is off.

but this is a small issue which I won't insist, so:

Reviewed-by: Kevin Tian <kevin.tian@intel.com>