> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Tuesday, February 7, 2023 9:27 PM > > > > > > No, I mean why can't vfio just call iommufd exactly once regardless of > > > what mode it is running in? > > > > This seems to be moving the DMA owner claim out of > iommufd_device_bind(). > > Is it? Then either group and cdev can claim DMA owner with their own > DMA > > marker. > > No, it has nothing to do with DMA ownership > > Just keep a flag in vfio saying it is in group mode or device mode and > act accordingly. It cannot be a simple flag. needs to be a refcnt since multiple devices in the group might be opened via cdev so the device mode should be cleared only when the last device via cdev is closed. Yi actually did implement such a flavor before, kind of introducing a vfio_group->cdev_opened_cnt field. Then cdev bind_iommufd checks whether vfio_group->opened_file has been set in the group open path. If not then increment vfio_group->cdev_opened_cnt. cdev close decrements vfio_group->cdev_opened_cnt. group open checks whether vfio_group->cdev_opened_cnt has been set. If not go to set vfio_group->opened_file. In this case only one path can claim DMA ownership. Is above what you expect? > > The iommufd DMA owner check is *only* to be used for protecting > against two unrelated drivers trying to claim the same device. > this is just one implementation choice. I don't see why it cannot be extended to allow one driver to protect against two internal paths. Just simply allow the driver to assign an owner instead of assuming iommufd_ctx.
