Re: [Xen-devel] [BUG] pci: mixed allocation pf and non-pf PCI MEM BAR (OVMF crash)

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.04.19 at 19:00, <igor.druzhinin@xxxxxxxxxx> wrote:
> As to hvmloader, coexisting of prefetchable and non-prefetchable BARs in
> a single aperture is perfectly normal from PCI specification point of
> view (e.g. see "PCI-TO-PCI BRIDGE ARCHITECTURE SPECIFICATION, REV 1.2").

After my earlier response I too have been thinking about this some
more. Looking at the spec, I can't seem to find any statement either
to the effect of what you say, or to the effect of the opposite. From
the text one might imply that putting prefetchable regions inside a
non-prefetchable bridge window ought to be acceptable, albeit
perhaps inefficient. But of course that's limited to cases where all
BARs can be fit below 4Gb.

But I don't think that spec is applicable here at all, as long as we
don't emulate any PCI-to-PCI bridges. There are only a host bridge,
a PCI-to-ISA one, and a "misc" one (the PM functions of PIIX4)
right now.

In any event I agree that at present mixing types ought to be fine.
This would likely change once we finally gain support for emulating
something like the Q35.

Jan



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