On Sun, May 25, 2014 at 12:16:20PM +0200, Alexander Graf wrote: > > On 24.05.14 05:12, Alexey Kardashevskiy wrote: > >On 05/24/2014 07:15 AM, Alexander Graf wrote: > >>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 <da...@gibson.dropbear.id.au> > >>>>>>> > >>>>>>>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 <da...@gibson.dropbear.id.au> > >>>>>>>Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > >>>>>>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. > >Nothing special. We attach group to address space by trying to add a group > >to every container in that address space. If it fails, we create a new > >container, put new group into it and attach container to the VFIO address > >space. The point here is we attach group to address space. > > > >We could still have a global containers list and when adding a group, loop > >through the global list of containers and look at the AS they are attached > >to but the logical structure AS->container->group->device remains the same. > > I honestly still have no idea what all of this is doing and why we can't > model it with PCI buses' IOMMU ASs. Alex, do you grasp it?
It's a while since I looked at this, so I may be forgetting.
But, I think it's simply a place to store the VFIO-specific
per-address-space information.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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