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

[Dave Hansen <dave.hansen@intel.com>]

On 4/25/22 06:53, Jean-Philippe Brucker wrote:
> On Sat, Apr 23, 2022 at 07:13:39PM +0800, zhangfei.gao@foxmail.com 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().

Yeah, this is a bit gnarly for -rc4.  Let's just make sure there's
nothing else simple we can do.

How does the IOMMU hardware know that all activity to a given PASID is
finished?  That activity should, today, be independent of an mm or a
fd's lifetime.