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

Liu, Yi L
2023-02-28T14:01:52Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Tuesday, February 28, 2023 9:44 PM
>
> On Tue, Feb 28, 2023 at 01:36:24PM +0000, Liu, Yi L wrote:
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > Sent: Tuesday, February 28, 2023 9:26 PM
> > >
> > > On Tue, Feb 28, 2023 at 01:22:50PM +0000, Liu, Yi L wrote:
> > >
> > > > > A null iommufd pointer and a bound df flag is sufficient to see that
> > > > > it is compat mode.
> > > >
> > > > Hope df->is_cdev_device suits your expectation.:-) The code will look
> > > > like below:
> > >
> > > Yes, this is better.. However I'd suggest 'uses_container' as it is
> > > clearer what the special case is
> >
> > Surely doable. Need to add a helper like below:
> >
> > bool vfio_device_group_uses_container()
> > {
> > lockdep_assert_held(&device->group->group_lock);
> > return device->group->container;
> > }
>
> It should come from the df.
>
> If you have a df then by definition:
> smp_load_acquire(..) == false - Not bound
> df->device->iommufd_ctx != NULL - Using iommufd
> df->group->containter != NULL - Using legacy container
> all other cases - NO_IOMMU
>
> No locking required since all these cases after the smp_load_acquire
> must be fixed for the lifetime of the df.

Do you mean the df->access_granted (introduced in patch 07) or a new flag?
Following your suggestion, it seems a mandatory requirement to do the
smp_load_acquire(..) == false check first, and then call into the vfio_device_open()
which further calls vfio_device_first_open() to check the iommufd/
legacy container/noiommu stuffs. Is it?

df->group->containter this may need a helper to avoid decoding group
field. May be just store container in df?

Regards,
Yi Liu