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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 04 September 2018 09:47
> To: Kevin Tian <kevin.tian@xxxxxxxxx>
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>; Julien Grall
> <julien.grall@xxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Stefano
> Stabellini <sstabellini@xxxxxxxxxx>; xen-devel <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH v6 01/14] iommu: introduce the concept of
> BFN...
> 
> >>> 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.

So your concern is cascaded IOMMUs?

  Paul

> 
> Jan
> 


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