[Qemu-devel] Re: [RFC PATCH 4/7] ide: IOMMU support

[Eduard - Gabriel Munteanu]

On Wed, Jul 14, 2010 at 02:53:03PM +0100, Paul Brook wrote:
> > Memory accesses must go through the IOMMU layer.
> 
> No. Devices should not know or care whether an IOMMU is present.

They don't really care. iommu_get() et al. are convenience functions
which can and do return NULL when there's no IOMMU and device code can
pass that NULL around without checking. I could've probably made the r/w
functions take only the DeviceState in addition to normal args, but
wanted to avoid looking up the related structures on each I/O operation.

> You should be adding a DeviceState argument to cpu_physical_memory_{rw,map}. 
> This should then handle IOMMU translation transparently.
> 
> You also need to accomodate the the case where multiple IOMMU are present.
> 
> Paul

We don't assume there's a single IOMMU in the generic layer. The
callbacks within 'struct iommu' could very well dispatch the request to
one of multiple, coexisting IOMMUs.


        Eduard