> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Friday, January 20, 2023 4:47 AM
>
> On Tue, 17 Jan 2023 05:49:37 -0800
> Yi Liu <yi.l.liu@xxxxxxxxx> wrote:
>
> > Allow the vfio_device file to be in a state where the device FD is
> > opened but the device cannot be used by userspace (i.e.
> its .open_device()
> > hasn't been called). This inbetween state is not used when the device
> > FD is spawned from the group FD, however when we create the device FD
> > directly by opening a cdev it will be opened in the blocked state.
> >
> > In the blocked state, currently only the bind operation is allowed,
> > other device accesses are not allowed. Completing bind will allow user
> > to further access the device.
> >
> > This is implemented by adding a flag in struct vfio_device_file to mark
> > the blocked state and using a simple smp_load_acquire() to obtain the
> > flag value and serialize all the device setup with the thread accessing
> > this device.
> >
> > Due to this scheme it is not possible to unbind the FD, once it is bound,
> > it remains bound until the FD is closed.
> >
> > Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> > ---
> > drivers/vfio/vfio.h | 1 +
> > drivers/vfio/vfio_main.c | 29 +++++++++++++++++++++++++++++
> > 2 files changed, 30 insertions(+)
> >
> > diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> > index 3d8ba165146c..c69a9902ea84 100644
> > --- a/drivers/vfio/vfio.h
> > +++ b/drivers/vfio/vfio.h
> > @@ -20,6 +20,7 @@ struct vfio_device_file {
> > struct vfio_device *device;
> > struct kvm *kvm;
> > struct iommufd_ctx *iommufd;
> > + bool access_granted;
> > };
> >
> > void vfio_device_put_registration(struct vfio_device *device);
> > diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> > index 3df71bd9cd1e..d442ebaa4b21 100644
> > --- a/drivers/vfio/vfio_main.c
> > +++ b/drivers/vfio/vfio_main.c
> > @@ -430,6 +430,11 @@ int vfio_device_open(struct vfio_device_file *df)
> > }
> > }
> >
> > + /*
> > + * Paired with smp_load_acquire() in vfio_device_fops::ioctl/
> > + * read/write/mmap
> > + */
> > + smp_store_release(&df->access_granted, true);
>
> Why is this happening outside of the first-open branch? Thanks,
The reason is the group path allows multiple device fds. But only
the first device fd open instance will trigger the first-open branch. But
all the device fd open instances need to set the access_granted
flag. Surely for the cdev path, this can be moved to the first-open
branch as cdev path only allows one device fd open.
Regards,
Yi Liu
