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Date: Tue, 13 Jan 2015 18:01:53 +0100
From: Alexander Graf <agraf@suse.de>
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Subject: Re: [Qemu-devel] [PATCH 0/1] pci: allow 0 address for PCI IO/MEM
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To: "Michael S. Tsirkin" <mst@redhat.com>, Michael Roth <mdroth@linux.vnet.ibm.com>
Cc: peter.maydell@linaro.org, aik@ozlabs.ru, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, pbonzini@redhat.com, hw.claudio@gmail.com, david@gibson.dropbear.id.au

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