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Date: Thu, 10 Apr 2014 14:13:56 +0200
From: Alexander Graf <agraf@suse.de>
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Subject: Re: [Qemu-devel] [PATCH v5 08/11] spapr-iommu: add SPAPR VFIO IOMMU
	device
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To: Alexey Kardashevskiy <aik@ozlabs.ru>, Alexander Graf <agraf@suse.com>, Alex Williamson <alex.williamson@redhat.com>
Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org


On 07.04.14 06:07, Alexey Kardashevskiy wrote:
> 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?

We need to handle in-kernel TCE tables with the emulated device IOMMU as 
well, so I'd

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

... which means you get H_GET_TCE for free as well ;).


Alex