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Date: Tue, 04 Nov 2014 17:30:14 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH for-2.1 2/2] acpi: mark ACPI tables ROM
 blob as extend-able on migration
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To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Igor Mammedov <imammedo@redhat.com>
Cc: peter.maydell@linaro.org, qemu-stable@nongnu.org, lersek@redhat.com, qemu-devel@nongnu.org, mst@redhat.com

On 03/11/2014 18:36, Dr. David Alan Gilbert wrote:
>   1) It's a block of data that's never mapped into the guests address
> space
>   2) It can change, but only at guest reset
>   3) Worst case is it can get upto about 2MB in size
> 
> it's pretty marginal whether this thing should be a RAMBlock,
> it doesn't feel like normal RAM or ROM in most ways; but there
> again 2MB is getting a bit large for the device state; hmm.

And also I think changing migration format gratuitously is bad.  We
decided to make these RAMs, which has some advantages and turned out to
have some possible disadvantages, but it's not a big deal.  They are
some kind of EPROM if you wish.

The important point is that we can (and arguably _should_ since it keeps
us honest!) make these ACPI tables RAMBlocks fixed-size per machine
type.  See the patches I posted around late September/early October.
There is no need to support auto-fixing of the RAMBlock's sizes.

Paolo