Re: [Qemu-devel] Recent SeaBIOS too big for QEMU -initrd

[Michael S. Tsirkin]

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 just sent a patch
        [PATCH] pc: reserve more memory for ACPI for new machine types
to do exactly that: double the acpi memory for 2.1 and up.

Would appreciate testing.

-- 
MST