Re: [Qemu-devel] About AddressSpace in intel-iommu emulation

[Paolo Bonzini]

Il 26/06/2014 16:01, Le Tan ha scritto:
> Hi Paolo,
> I am adding intel-iommu emulation to q35 for the GSoC project. I am
> confused about AddressSpace and I believe that you can help me. :)
> 1. For intel-iommu emulation, I have to read the translation
> structures from guest memory, that is, the guest will prepare some
> tables in memory and write the physical address of them to a register
> of intel-iommu, and I need to access those structures. I use
> dma_memory_read(&address_space_memory,...) to do this. Is that right?
> I am not sure that whether accesses to address_space_memory will be
> translated through IOMMU. I think the answer is not, because I see
> that cpu_physical_memory_read() also use address_space_memory as
> AddressSpace.

Correct.

> 2. In my opinion, I have to init a AddressSpace and link it with my
> IOMMU MemoryRegion, then the bus uses this AddressSpace to translate
> the accesses. Is that right? For q35, how can I register my IOMMU
> MemoryRegion to the bus? I see that there is function
> pci_setup_iommu() that links a AddressSpace to the bus to translate
> accesses to PCI into system memory. Is that related? I think q35
> should maintain a bus AddressSpace, but I can't find it.
> What do you think?

Right now, the q35 PCI host does not define an iommu_fn, so the default 
DMA address space is used by pci_device_iommu_address_space.  This is 
just address_space_memory.

The iommu_fn is set with pci_setup_iommu.  Commit ae74bbe (apb: 
implement IOMMU translation for PCI host bridge, 2014-05-28) provides an 
example of how to prepare an IOMMU memory region, add it to an address 
space, and return that address space from an iommu_fn.

Thanks,

Paolo

> Thanks very much!
>
> Regards,
> Le Tan