Re: [Qemu-ppc] [Qemu-devel] [PATCH v6 5/7] vfio: Introduce VFIO address spaces

[Alexander Graf]

On 23.05.14 18:16, Alexey Kardashevskiy wrote:
> On 05/23/2014 10:05 PM, Alexander Graf wrote:
> > On 23.05.14 14:03, Alexey Kardashevskiy wrote:
> > > On 05/23/2014 09:28 PM, Alexander Graf wrote:
> > > > On 23.05.14 06:59, Alexey Kardashevskiy wrote:
> > > > > From: David Gibson <address@hidden>
> > > > >
> > > > > The only model so far supported for VFIO passthrough devices is the model
> > > > > usually used on x86, where all of the guest's RAM is mapped into the
> > > > > (host) IOMMU and there is no IOMMU visible in the guest.
> > > > >
> > > > > This patch begins to relax this model, introducing the notion of a
> > > > > VFIOAddressSpace.  This represents a logical DMA address space which will
> > > > > be visible to one or more VFIO devices by appropriate mapping in the
> > > > > (host)
> > > > > IOMMU.  Thus the currently global list of containers becomes local to
> > > > > a VFIOAddressSpace, and we verify that we don't attempt to add a VFIO
> > > > > group to multiple address spaces.
> > > > >
> > > > > For now, only one VFIOAddressSpace is created and used, corresponding to
> > > > > main system memory, that will change in future patches.
> > > > >
> > > > > Signed-off-by: David Gibson <address@hidden>
> > > > > Signed-off-by: Alexey Kardashevskiy <address@hidden>
> > > > Don't we already have a DMA address space in the PCI bus? We could just use
> > > > that one instead, no?
> > > I do not know about x86, but for spapr that VFIOAddressSpace is nothing but
> > > wrapper around an AddressSpace from the SPAPR PHB.
> > So why do we need that wrapper? Can't we just use the PHB's AddressSpace?
> > There's a good chance I'm not grasping something here :).
>
> We cannot attach VFIO containers (aka "groups" or "PEs" for spapr) to
> AddressSpace, there is nothing like that in AddressSpace/MemoryRegion API
> as this container thing is local to VFIO.

Ok, please explain how this AddressSpace is different from the VFIO 
device's parent's IOMMU DMA AddressSpace and why we need it.


Alex