Re: [v1 1/2] xen/p2m: Create identity mappings for PFNs beyound E820 and PCI BARs

Jan Beulich
2013-10-29T15:30:25Z

>>> On 29.10.13 at 16:11, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> On Tue, Oct 29, 2013 at 02:55:13PM +0000, Jan Beulich wrote:
>> >>> On 29.10.13 at 15:45, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
>> > On Tue, Oct 29, 2013 at 08:23:30AM +0000, Jan Beulich wrote:
>> >> >>> On 28.10.13 at 17:58, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
>> >> > On Fri, Oct 25, 2013 at 04:08:19PM -0600, Bjorn Helgaas wrote:
>> >> >> If you can look at PCI host bridge apertures instead of BARs, that
>> >> >> would solve both problems. Reassigning those apertures is
>> >> >> theoretically possible but is not even a gleam in our eyes yet.
>> >> >
>> >> > <nods> I think I have to have both (BARs and host bridge apertures) as when
>> >> > we do PCI passthrough to a guest - we might do it without a bridge.
>> >>
>> >> Why? Aren't the host bridge ranges necessarily a superset of the
>> >> individual devices' BARs?
>> >
>> > Yes. But when you pass in a PCI device to a PV guest you don't pass in the
>> > bridge. Just the PCI device itself.
>>
>> Right you are. Which means that basing the whole logic on the
>> PCI device BARs is likely wrong anyway, not just because it
>> doesn't account for other MMIO ranges.
>
> Right, but that is OK. When you pass in a PCI device to a PV guest you
> only care about that specific device driver being able to access its BARs.

Yes, but again - this is not the only possible way of allowing a
guest access to MMIO. See the "iomem" config option.

Jan