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[Qemu-devel] [0/8] RFC: VFIO and guest side IOMMUs, revisited

From: David Gibson
Subject: [Qemu-devel] [0/8] RFC: VFIO and guest side IOMMUs, revisited
Date: Mon, 13 May 2013 20:54:17 +1000


Here's another spin on my patches working towards integrating vfio
with guest visible iommu support.  These are on top of Paolo Bonzini's
iommu branch at:

This new spin starts with some extensions to the pci / memory API
core, then some VFIO updates to use those to start breaking vfio's
assumption of mapping system memory directly.

It doesn't actually support guest IOMMUs with vfio yet, but it does
support simpler non-identify DMA mappings between PCI space and main
memory, such as RAM being mapped at a non-zero offset within PCI space
(this is configurable on many embedded host bridges).  This new spin
no longer adds vfio specific hooks into the memory core, which turns
out to be less messy than I anticipated, though it may yet get worse
with actual guest IOMMU support, which I'm still working on.

Aside: I realised there's another problem with assignment of DMA
address spaces in the current DMAContext scheme which is still there
with the iommu rework, but it's more or less orthogonal to the changes
here, so I've left it for now.  Specifically the way the iommu is
determined from a callback in the PCIBus means that it won't be
assigned for devices under a PCI-PCI bridge.

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