Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit

From: Jean-Philippe Brucker
Date: Mon Apr 25 2022 - 09:54:17 EST

On Sat, Apr 23, 2022 at 07:13:39PM +0800, zhangfei.gao@xxxxxxxxxxx wrote:
> > > On 5.17
> > > fops_release is called automatically, as well as iommu_sva_unbind_device.
> > > On 5.18-rc1.
> > > fops_release is not called, have to manually call close(fd)
> > Right that's weird
> Looks it is caused by the fix patch, via mmget, which may add refcount of
> fd.

Yes indirectly I think: when the process mmaps the queue, mmap_region()
takes a reference to the uacce fd. That reference is released either by
explicit close() or munmap(), or by exit_mmap() (which is triggered by
mmput()). Since there is an mm->fd dependency, we cannot add a fd->mm
dependency, so no mmget()/mmput() in bind()/unbind().

I guess we should go back to refcounted PASIDs instead, to avoid freeing
them until unbind().