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

[Jason Gunthorpe]

On Thu, May 13, 2021 at 04:07:07PM +1000, David Gibson wrote:
> On Wed, May 05, 2021 at 01:39:02PM -0300, Jason Gunthorpe wrote:
> > On Wed, May 05, 2021 at 02:28:53PM +1000, Alexey Kardashevskiy wrote:
> > 
> > > 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.
> > 
> > That specific use case doesn't really need a vIOMMU though, does it?
> 
> Possibly not, but the mechanics needed to do vIOMMU on different host
> IOMMU aren't really different from what you need for a no-vIOMMU
> guest.  

For very simple vIOMMUs this might be true, but this new features of nesting
PASID, migration, etc, etc all make the vIOMMU complicated and
emuluating it completely alot harder.

Stuffing a vfio-pci into a guest and creating a physical map using a
single IOASID is comparably trivial.

Jason