On Mon, Feb 27, 2023 at 03:11:23AM -0800, Yi Liu 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. > > The reason for the inbetween state is that userspace only gets a FD but > doesn't gain access permission until binding the FD to an iommufd. So in > the blocked state, only the bind operation is 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. > > Following this lockless scheme, it can safely handle the device FD > unbound->bound but it cannot handle bound->unbound. To allow this we'd > need to add a lock on all the vfio ioctls which seems costly. So once > device FD 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> > Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx> > --- > drivers/vfio/group.c | 6 ++++++ > drivers/vfio/vfio.h | 1 + > drivers/vfio/vfio_main.c | 16 ++++++++++++++++ > 3 files changed, 23 insertions(+) Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Jason
