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Date: Thu, 24 Jul 2014 12:35:26 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC for-2.1 for for-2.0-stable] pc: acpi:
 generate AML only for PCI0 devices if PCI bridge hotplug is disabled
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To: Igor Mammedov <imammedo@redhat.com>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, mst@redhat.com, qemu-stable@nongnu.org, dgilbert@redhat.com, amit.shah@redhat.com, lersek@redhat.com

Il 24/07/2014 11:07, Igor Mammedov ha scritto:
> Fixes migration regression from QEMU-1.7 to a newer QEMUs.
> SSDT table size in QEMU-1.7 doesn't change regardless of
> a number of PCI bridge devices present at startup.
> 
> However in QEMU-2.0 since addition of hotplug on PCI bridges,
> each PCI bridge adds ~1875 bytes to SSDT table, including
> pc-i440fx-1.7 machine type where PCI bridge hotplug disabled
> via compat property.
> It breaks migration from "QEMU-1.7" to "QEMU-2.[01] -M pc-i440fx-1.7"
> since RAMBlock size of ACPI tables on target becomes larger
> then on source and migration fails with:
> 
> "Length mismatch: /rom@etc/acpi/tables: 2000 in != 3000"
> 
> error.

In principle, this definitely makes sense.  With QEMU-2.0 and 2.0.1 out
in the wild (and packaged into Ubuntu), however, it's difficult to
decide whether to include this patch or not.

I feel more like having downstreams include it if they skipped QEMU 2.0
and went straight from 1.7 to 2.1.

Paolo