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

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH v6 5/7] vfio: Introduce VFIO address spaces
Date: Fri, 23 May 2014 23:15:54 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

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
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.


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