Re: [Qemu-devel] [PATCH v5 08/11] spapr-iommu: add SPAPR VFIO IOMMU device

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 04/03/2014 11:17 PM, Alexander Graf wrote:
> 
> On 12.03.14 06:52, Alexey Kardashevskiy wrote:
>> This adds SPAPR VFIO IOMMU device in order to support DMA operations
>> for VFIO devices.
> 
> Sorry if this has been mentioned before, but why exactly do you need a
> separate IOMMU for VFIO? Couldn't the existing IOMMU backend drive things?

Well... Since I started VFIO on SPAPR, the emulated and VFIO IOMMU became
almost the same thing and I'll rework that too before I post things again.

However one difference still remains - IOMMU for emulated PCI and VIO keeps
a TCE table (allocated in QEMU or mmap'ed from the host kernel) and VFIO
IOMMU works with the table which is allocated and owned by the host kernel.

Since TCE tables are used only by devices, the IOMMU translation callback
is never called by VFIO devices and that's ok and I checked - it works.

So I either need a property in the IOMMU device to tell it is TCE table and
MemoryRegionIOMMUOps::translate() are required. Or a new IOMMU device
class. What to choose?

Oh. btw. There is H_GET_TCE now which I have to implement for VFIO :( This
will never ever end.


-- 
Alexey