Eric W. Biederman wrote:
> "Han, Weidong" <weidong.han@xxxxxxxxx> writes:
>
>> Ingo Molnar wrote:
>>> * Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
>>>
>>>> Not finding an upstream pcie_bridge and then concluding we are a
>>>> pcie device seems bogus.
>>>>
>>
>> If device is pcie, pci_find_upstream_pcie_bridge() will return
>> NULL. For root complex integrated device, it won't find upstream
>> bridge, and also return NULL. What's more, pcie device and root
>> complex integrated device will be handled as the same way to set
>> sid, so I mix them here. But it also returns NULL for busted
>> hardware. I think no parent bus can be considered Root Complex
>> integrated device, right? If so, I think can handle it as follows:
>
> I have problems with pci_find_upstream_pcie_bridge. The
> name is actively misleading about what that function does.
> Returning a pci_to_pci bridge is strongly counter intuitive
> give that name.
>
> Can we change it to pci_find_upstream_pcie_to_pci_bridge.
> Returning NULL in all cases when there is not an upstream
> pcie_to_pci bridge.
pci_find_upstream_pcie_bridge returns upstream pcie-to-pci/pcix bridge or legacy pci bridge for a pci device. pci_find_upstream_bridge may be more suitable.
>
> For the set_sid case that is ideal. For the other cases in
> intel-iommu.c it may be a problem. Is it even possible to have a
> genuine pci device not behind a pcie to pci bridge on an intel
> chipset with this iommu?
>
I think it's little possible. But coincide to VT-d spec, we need to handle differently for devices behind pcie-to-pci/pcix bridge and behind legacy pci bridge.
>
>> ...
>> if (dev->is_pcie || !dev->bus->parent) {
>> set_irte_sid(...);
>> return 0;
>> }
>>
>> bridge = pci_find_upstream_pcie_bridge(dev);
>> if (bridge) {
>> if (bridge->is_pcie) /* PCIE-to-PCI/PCIx bridge */
>> set_irte_sid(...); else /* legacy PCI bridge */
>> set_irte_sid(..);
>> }
>>
>> return 0;
>>
>>>> Why if we do have an upstream pcie bridge do we only want to do a
>>>> bus range verification instead of checking just for the bus
>>>>> devfn?
>>>>
>>>> The legacy PCI case seems even stranger.
>>
>> Why? If a PCI device isn't connected to a PCIe bridge, it should be
>> a legacy bridge.
>
> I am not deep in the IOV specification at the moment. I am mostly
> wondering why we pick the parts we pick to verify. I recall
> bus and devfn being on the pcie packets so that makes sense.
>
> Why would we ever want to do something different? Does a pcie to pci
> bridge do something different in it's translation?
source-id is different between devices pcie-to-pci/pcix bridge and behind legacy pci bridge. Thus VT-d needs to handle it differently.
The pcie-to-pci/pcix bridges may generate a different requester-id and tag combination in some instances for transactions forwarded to the bridge's PCI Express interface. The action of replacing the original transaction's requester-id with one assigned by the bridge is generally referred to as taking 'ownership' of the transaction. If the bridge generates a new requester-id for a transaction forwarded from the secondary interface to the primary interface, the bridge assigns the PCI Express requester-id using the secondary interface's bus number, and sets both the device number and function number fields to zero. Refer to the PCI Express-to-PCI/PCI-X bridge specifications for more details.
For devices behind conventional PCI bridges, the source-id in the DMA requests is the requester-id of the bridge device.
Regards,
Weidong
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