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Date:   Tue, 3 Nov 2020 09:23:35 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     "joro@8bytes.org" <joro@8bytes.org>
CC:     "Tian, Kevin" <kevin.tian@intel.com>,
        Jason Wang <jasowang@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
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Subject: Re: (proposal) RE: [PATCH v7 00/16] vfio: expose virtual Shared
 Virtual Addressing to VMs
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On Tue, Nov 03, 2020 at 02:18:52PM +0100, joro@8bytes.org wrote:
> On Tue, Nov 03, 2020 at 08:56:43AM -0400, Jason Gunthorpe wrote:
> > On Tue, Nov 03, 2020 at 10:52:09AM +0100, joro@8bytes.org wrote:
> > > So having said this, what is the benefit of exposing those SVA internals
> > > to user-space?
> > 
> > Only the device use of the PASID is device specific, the actual PASID
> > and everything on the IOMMU side is generic.
> > 
> > There is enough API there it doesn't make sense to duplicate it into
> > every single SVA driver.
> 
> What generic things have to be done by the drivers besides
> allocating/deallocating PASIDs and binding an address space to it?
> 
> Is there anything which isn't better handled in a kernel-internal
> library which drivers just use?

Userspace needs fine grained control over the composition of the page
table behind the PASID, 1:1 with the mm_struct is only one use case.

Userspace needs to be able to handle IOMMU faults, apparently

The Intel guys had a bunch of other stuff too, looking through the new
API they are proposing for vfio gives some flavour what they think is
needed..

Jason