Re: [Xen-devel] [PATCH v6 01/14] iommu: introduce the concept of BFN...

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.09.18 at 10:37, <kevin.tian@xxxxxxxxx> wrote:
>>  From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Tuesday, September 4, 2018 4:33 PM
>> >
>> > bus address is commonly used along with physical/virtual address, to
>> > represent different views between devices and CPU. From that angle
>> > I think BFN is a clear term in this context. btw it is not necessary to
>> > differentiate GBFN and MBFN since there is only one BFN view per
>> > device.
>> 
>> Sure, but you neglect the presence of one or more IOMMUs when
>> you say "between devices and CPU". There addresses prior to and
>> after IOMMU translation are distinct, and while the one before the
>> translation matches the device view, the one after translation does
>> not necessarily match the CPU view. Hence there are two "bus"
>> frame numbers here - one representing the device view, and the
>> other representing the IOMMU (output) view.
>> 
> 
> I didn't get. the output address from IOMMU is the one sent to
> memory controller, same as the one sent from CPU.

That's on present x86 systems, but aiui not in the general case. The
terminology to be used in Xen should fit the general case though.

Jan



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