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Date: Thu, 28 Aug 2014 23:46:21 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 08/12] pci: allow 0 address for PCI IO
 regions
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Alexey Kardashevskiy <aik@ozlabs.ru>, Alexander Graf <agraf@suse.de>, Michael Roth <mdroth@linux.vnet.ibm.com>, Mike Day <ncmike@ncultra.org>, "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, tyreld@linux.vnet.ibm.com, nfont@linux.vnet.ibm.com

On Thu, Aug 28, 2014 at 10:33:02PM +0100, Peter Maydell wrote:
> On 28 August 2014 22:21, Michael Roth <mdroth@linux.vnet.ibm.com> wrote:
> > But I guess there's still a separate issue, where there's a high liklihood that
> > a 0 address would conflict with some hard-wired IO address? Wouldn't this be a
> > guest bug though?

Real hardware behaves in a specific way.
the problem is we don't always emulate it properly, and PCI
has some work arounds for that.

> Even if it's a guest bug, we should act like the hardware does
> if the guest does this. If that differs between PCI controllers
> then we need a flag so the host controller model can select
> the required behaviour. (The versatile PB PCI controller we
> model does have "address 0 is valid", and we'd need to have
> this working if we implemented DMA accesses properly.)
> 
> -- PMM

Exactly.
Actually, I forgot that I might have already fixed it for PC:
83d08f2673504a299194dcac1657a13754b5932a
    pc: map PCI address space as catchall region for not mapped addresses

But need to go back and re-check other systems.


-- 
MST