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Date: Wed, 20 Aug 2014 13:27:25 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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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: Kevin OConnor <kevin@koconnor.net>, John Snow <jsnow@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@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.
> 
> The guest Linux kernel rejects the initrd:
> BIOS-provided physical RAM map:
>  BIOS-e820: 0000000000010000 - 000000000009fc00 (usable)
>  BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
>  BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
>  BIOS-e820: 0000000000100000 - 000000003ffe0000 (usable)
>  BIOS-e820: 000000003ffe0000 - 0000000040000000 (reserved)
>  BIOS-e820: 00000000feffc000 - 00000000ff000000 (reserved)
>  BIOS-e820: 00000000fffc0000 - 0000000100000000 (reserved)
> ...
> initrd extends beyond end of memory (0x3ffef79f > 0x3ffe0000)
> disabling initrd
> 
> It is easy enough to "fix" the problem by bumping ACPI_DATA_SIZE up to
> 0x20000 in QEMU.  Perhaps this should only be done for bios-256k.bin
> guests and not bios-128k.bin guests (QEMU 1.7 and older machine
> types).
> 
> 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.
> 
> Any ideas?
> 
> Stefan

I would say 2.1 and up, -M pc-i440fx-2.0 works fine, or am I mistaken?