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From: Pavel Fedin <p.fedin@samsung.com>
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Date: Wed, 29 Jul 2015 14:16:36 +0300
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Subject: Re: [Qemu-devel] [PATCH v3] hw/arm/virt: Add high MMIO PCI region
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To: 'Peter Maydell' <peter.maydell@linaro.org>
Cc: 'QEMU Developers' <qemu-devel@nongnu.org>, 'Igor Mammedov' <imammedo@redhat.com>, 'Paolo Bonzini' <pbonzini@redhat.com>, 'Alexander Graf' <agraf@suse.de>, "'Michael S. Tsirkin'" <mst@redhat.com>

 Hello!

> It matters because you can run 32 bit guests in 64-bit-capable
> CPUs.

 Yes, i know.

> I don't really want to have two different address layouts
> just to work around a kernel bug

 They will not be really different. Just for 32-bit machines there will =
be no second MMIO window, and for 64-bit ones there will be. Nothing =
else will be different.

> if we could fix the kernel bug instead...

 We could. But what about existing installations? They will be forced to =
upgrade kernels, we will not have backwards compatibility option. And =
users will complain that "my old VM stopped working with new qemu".
 Well, this discussion seems to be stuck, so let's move on. What is your =
final word? Options are:
1. Include second region unconditionally. Old 32-bit guests will stop =
working.
2. Add machine option to specify second region size. For 64-bits it will =
default to something, for 32-bits it will default to 0 (=3D off). It =
will be possible to turn on the region for 32-bit machines explicitly.
3. Include second region only on 64-bit guests. 32-bit ones will wait =
until somebody needs it.

 Your choice ?

 P.S. My 3.19 guest has LPAE disabled in the configuration. Perhaps my =
fault, but still it's a potential problem.
=20

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia