Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

[Alexey Kardashevskiy]

On 05/05/2021 04:15, Jason Gunthorpe wrote:
> On Tue, May 04, 2021 at 01:54:55PM +1000, David Gibson wrote:
> > On Mon, May 03, 2021 at 01:05:30PM -0300, Jason Gunthorpe wrote:
> > > On Thu, Apr 29, 2021 at 01:20:22PM +1000, David Gibson wrote:
> > > > > There is a certain appeal to having some
> > > > > 'PPC_TCE_CREATE_SPECIAL_IOASID' entry point that has a wack of extra
> > > > > information like windows that can be optionally called by the viommu
> > > > > driver and it remains well defined and described.
> > > >
> > > > Windows really aren't ppc specific.  They're absolutely there on x86
> > > > and everything else as well - it's just that people are used to having
> > > > a window at 0..<something largish> that you can often get away with
> > > > treating it sloppily.
> > >
> > > My point is this detailed control seems to go on to more than just
> > > windows. As you say the vIOMMU is emulating specific HW that needs to
> > > have kernel interfaces to match it exactly.
> >
> > It's really not that bad.  The case of emulating the PAPR vIOMMU on
> > something else is relatively easy, because all updates to the IO page
> > tables go through hypercalls.  So, as long as the backend IOMMU can
> > map all the IOVAs that the guest IOMMU can, then qemu's implementation
> > of those hypercalls just needs to put an equivalent mapping in the
> > backend, which it can do with a generic VFIO_DMA_MAP.
>
> So you also want the PAPR vIOMMU driver to run on, say, an ARM IOMMU?


This is a good feature in general when let's say there is a linux 
supported device which has a proprietary device firmware update tool 
which only exists as an x86 binary and your hardware is not x86 - 
running qemu + vfio in full emulation would provide a way to run the 
tool to update a physical device.


--
Alexey