Re: [Xen-devel] RFC: [PATCH 1/3] Enhance platform support for PCI

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.02.15 at 16:46, <ian.campbell@xxxxxxxxxx> wrote:
> On Mon, 2015-02-23 at 15:27 +0000, Jan Beulich wrote:
>> >>> On 23.02.15 at 16:02, <ian.campbell@xxxxxxxxxx> wrote:
>> > Is the reason for the scan being of segment 0 only is that it is the one
>> > which lives at the legacy PCI CFG addresses (or those magic I/O ports)? 
>> 
>> Right - ideally we would scan all segments, but we need Dom0 to
>> tell us which MMCFG regions are safe to access,
> 
> Is this done via PHYSDEVOP_pci_mmcfg_reserved?

Yes.

>>  and hence can't
>> do that scan at boot time. But we also won't get away without
>> scanning, as we need to set up the IOMMU(s) to at least cover
>> the devices used for booting the system.
> 
> Which hopefully are all segment 0 or aren't needed until after dom0
> tells Xen about them I suppose.

Right. With EFI one may be able to overcome this one day, but the
legacy BIOS doesn't even surface mechanisms (software interrupts)
to access devices outside of segment 0.

>>  (All devices on segment zero are supposed to
>> be accessible via config space access method 1.)
> 
> Is that "the legacy ....  or magic ..." again?

Yes (just that there are two of them).

Jan


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