[PATCH 0/2] iommu: Remove iommu_sva_ops::mm_exit()
jacob.jun.pan at linux.intel.com
Fri Apr 10 02:21:34 AEST 2020
On Thu, 9 Apr 2020 11:25:19 -0300
Jason Gunthorpe <jgg at 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
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