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Il 13/05/2013 15:13, David Gibson ha scritto:
> On Mon, May 13, 2013 at 02:23:30PM +0200, Paolo Bonzini wrote:
>> Il 13/05/2013 12:54, David Gibson ha scritto:
>>> 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.
>>
>> Right. I saw the report from Alexey, but I am a bit wary of
>> touching it because it's not a regression. In fact there is
>> even a FIXME for it:
>>
>> /* FIXME: inherit memory region from bus creator */
>
> Uh.. sort of.
>
>> Perhaps we can make pci_iommu_as a Bus method, where the default
>> implementation looks up along the chain, and the end of the
>> recursion is in SysBus or in PCI buses that have set the
>> callback.
>
> So, this is complicated by the fact that there are two cases, and
> they can both be found in existing hardware.
>
> 1) One is where devices behind the bridge are not visible /
> differentiable to the IOMMU, and so effectively all their DMAs
> originate from the bridge device itself. In this case the correct
> thing is to give all devices under the bridge the same DMA
> AddressSpace as the bridge device, as suggested by the FIXME. This
> will be typical behaviour for PCI-E to PCI bridges.
>
> 2) The other case is where the bridge passes through RIDs, so that
> the IOMMU can still differentiate devices behind it. For this
> case, we really want the hook to be in the host bridge / root bus,
> and it can make a decision based on the full bus/dev/fn
> information. This will be typical for PCI-E to PCI-E bridges (or
> switches or nexuses or whatever they're usually called for PCI-E).
> This case will be very important as we start to model newer PCI-E
> based machines by default, where typically *all* devices are
> behind a logical p2p bridge inside the root complex (but are still
> differentiable by the Intel IOMMU amongst others).
>
> I'm not sure at this stage how to properly handle both cases.
Suppose you have a host bridge pci_bus0 and a PCIE->PCIE bridge
pci_bus1. pci_bus1 does not define a IOMMU callback, pci_bus0 does.
Would it work to use the PCIBus callback provided by pci_bus0, but
invoke it as
pci_bus0->iommu_fn(pci_bus1, pci_bus0->iommu_opaque, devfn)
?
Paolo
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