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

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Date:	Tue, 29 Oct 2013 14:55:13 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:	"David Vrabel" <david.vrabel@...rix.com>,
	<Santosh.Jodh@...rix.com>, "Bjorn Helgaas" <bhelgaas@...gle.com>,
	<xhejtman@....muni.cz>,
	"xen-devel" <xen-devel@...ts.xensource.com>,
	<boris.ostrovsky@...cle.com>, <mukesh.rathor@...cle.com>,
	<yuval.shaia@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [v1 1/2] xen/p2m: Create identity mappings for PFNs
 beyound E820 and PCI BARs

>>> On 29.10.13 at 15:45, Konrad Rzeszutek Wilk <konrad.wilk@...cle.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@...cle.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.

Jan

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