[Xen-devel] RE: co-assignment needs for PCI devices

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> "Cui, Dexuan" <dexuan.cui@xxxxxxxxx> 31.03.09 09:48 >>>
>Jan Beulich wrote:
>> Also, being not really knowledgeable about all the differences between
>> PCIe and PCI, I'd appreciate some clarification on why on PCIe it is
>> possible and correct to do a secondary bus reset when targeting just
>> the (PCIe) functions of a single device - to me this seems to imply
>> that there's a one-device-per-non-root-bus restriction there.
>According to VT-d spec (section 3.6.1: Identifying Origination of DMA 
>Requests), PCI devices behind the same uppermost PCI/PCI-X
>bridge must be co-assigned to the same guest. PCIe devices have not such a 
>constraint.
>
>FLR (Functional Level Reset) is used to quiesce an assigned device when we 
>destroy a guest or we detach the device from the guest.
>If a PCIe device has no standard FLR capability, we'll try to use 
>SecondaryBusReset as a way to do FLR. Unluckily,
>SecondaryBusReset resets all the devices behind the bridge, so for a 
>multi-function PCIe device without FLR capability, we require
>they have to be co-assigned to the same guest --  certainly this is only for 
>iommu case and for non-iommu case this requirement may
>be not proper and we shoud fix it...

But - for the sake of my education, if you forgive - you didn't answer whether 
there is a one-device-per-secondary-bus restriction on PCIe...

Thanks, Jan


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