Re: [PATCH 2/2] iommu/sva: Remove mm parameter from SVA bind API

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

Hi Jean,

On Fri, 9 Apr 2021 11:03:05 -0700, Jacob Pan
<jacob.jun.pan@linux.intel.com> wrote:

> > problems:
> > 
> > * We don't have a use-case for binding the mm of a remote process (and
> >   it's supposedly difficult for device drivers to do it securely). So
> > OK, we remove the mm argument from iommu_sva_bind_device() and use the
> >   current mm. But the IOMMU driver isn't going to do
> > get_task_mm(current) every time it needs the mm being bound, it will
> > take it from iommu_sva_bind_device(). Likewise iommu_sva_alloc_pasid()
> > shouldn't need to bother with get_task_mm().
> > 
> > * cgroup accounting for IOASIDs needs to be on the current task.
> > Removing the mm parameter from iommu_sva_alloc_pasid() doesn't help
> > with that. Sure it indicates that iommu_sva_alloc_pasid() needs a
> > specific task context but that's only for cgroup purpose, and I'd
> > rather pass the cgroup down from iommu_sva_bind_device() anyway (but am
> > fine with keeping it within ioasid_alloc() for now). Plus it's an
> > internal helper, easy for us to check that the callers are doing the
> > right thing. 
> With the above split, we really just have one allocation function:
> ioasid_alloc(), so it can manage current cgroup accounting within. Would
> this work?
After a few attempts, I don't think the split can work better. I will
restore the mm parameter and add a warning if mm != current->mm.

Thanks,

Jacob