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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

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 <david@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 <david@gibson.dropbear.id.au>
>>>> Signed-off-by: Alexey Kardashevskiy <aik@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.



-- 
Alexey