Re: [PATCH 0/2] iommu: Remove iommu_sva_ops::mm_exit()

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

On Thu, 9 Apr 2020 11:25:19 -0300
Jason Gunthorpe <jgg@ziepe.ca> wrote:

> On Thu, Apr 09, 2020 at 07:14:24AM -0700, Jacob Pan wrote:
> > > When the process is killed, mm release can happen before fds are
> > > released. If you look at do_exit() in kernel/exit.c:
> > > 
> > > 	exit_mm()
> > > 	  mmput()  
> > > 	   -> mmu release notifier    
> > > 	...
> > > 	exit_files()
> > > 	  close_files()
> > > 	    fput()
> > > 	exit_task_work()
> > > 	  __fput()  
> > > 	   -> unbind()    
> > >   
> > So unbind is coming anyway, the difference in handling in mmu
> > release notifier is whether we silently drop DMA fault vs.
> > reporting fault?  
> 
> Userspace can significantly delay the final fput triggering the
> unbind, the above is only for the trivial case where the process
> owning the mm_struct is the only process holding the fd.
> 
Are you talking about FDs owned buy children after fork() or FDs sent
over to another process. I think, in either case SVA is not supported.

> The destruction of a mm_struct should be treated the same as unmapping
> every vma in the process. The observable effect should be no different
> than munmap.
> 
Good point. I agree, we should suppress the error in the window before
unbind.

> Jason

[Jacob Pan]
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