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Date: Wed, 20 Aug 2014 18:17:40 -0400
From: Kevin O'Connor <kevin@koconnor.net>
Message-ID: <20140820221739.GA10152@morn.localdomain>
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Subject: Re: [Qemu-devel] Recent SeaBIOS too big for QEMU -initrd
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>, John Snow <jsnow@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, "Michael S. Tsirkin" <mst@redhat.com>

On Wed, Aug 20, 2014 at 11:27:41AM +0100, Stefan Hajnoczi wrote:
> The QEMU -initrd option loads the initrd at the top of RAM.  There is
> a 64 KB safety region for ACPI tables in hw/i386/pc.c:load_linux():
> 
>   initrd_max = max_ram_size-ACPI_DATA_SIZE-1;
> 
> QEMU's bios-256k.bin SeaBIOS build reserves 128 KB at the top of
> memory so the 64 KB ACPI data size has become too small.

Just to clarify, SeaBIOS uses a variable amount of data at the top of
ram.  SeaBIOS isn't changing the allocation because of its build
parameters, but because QEMU is passing more ACPI tables to it.

> Perhaps QEMU -> SeaBIOS -> linuxboot.bin can be simplified so QEMU
> doesn't have to guess what e820 region SeaBIOS will reserve.
> linuxboot.bin would probably be the place to do it unless SeaBIOS has
> Linux loading functionality that could be reused.

There is no current functionality in SeaBIOS to deploy a Linux kernel
from fw_cfg.  However, it looks like it would be pretty simple to add
if someone wants to give it a try.

-Kevin