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

[Alexander Graf <agraf@suse.de>]

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 <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.

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


Alex