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Date: Tue, 13 Jan 2015 20:42:28 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 0/1] pci: allow 0 address for PCI IO/MEM
 regions
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To: Alexander Graf <agraf@suse.de>
Cc: peter.maydell@linaro.org, aik@ozlabs.ru, Michael Roth <mdroth@linux.vnet.ibm.com>, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, pbonzini@redhat.com, hw.claudio@gmail.com, david@gibson.dropbear.id.au

On Tue, Jan 13, 2015 at 06:01:53PM +0100, Alexander Graf wrote:
> On 01/13/15 17:17, Michael S. Tsirkin wrote:
> >On Tue, Jan 13, 2015 at 05:54:46PM +0200, Michael S. Tsirkin wrote:
> >>I think we already do this for PC:
> >>	commit 83d08f2673504a299194dcac1657a13754b5932a
> >>	Author: Michael S. Tsirkin <mst@redhat.com>
> >>	Date:   Tue Oct 29 13:57:34 2013 +0100
> >>
> >>	    pc: map PCI address space as catchall region for not mapped addresses
> >>
> >>but we need to find and fix all other targets.
> >BTW this is very easy to test.
> >Add an unused device (like ivshmem) enable BAR, and set it to 0.
> >System should survive, as opposed to hanging.
> >
> >But the big question is whether this is the right
> >thing to do for each platform.
> >For PIIX whatever is not system memory, is PCI.
> >But other boxes might have a different view of the matter.
> 
> Only few platforms have PCI mapped at 0, no? So in most cases you get
> windows that simply don't have overlapping at all.
> 
> 
> Alex

What's missing is complete analysis of the problem.
Ideally testing on several targets.

-- 
MST