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 11:11:29 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Jan Beulich <JBeulich@...e.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 Tue, Oct 29, 2013 at 02:55:13PM +0000, Jan Beulich wrote:
> >>> 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.

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.

> 
> Jan
> 
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