Re: [Xen-devel] [BUG 1747]Guest could't find bootable device with memory more than 3600M

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Sat, Jun 8, 2013 at 8:27 AM, Hao, Xudong <xudong.hao@xxxxxxxxx> wrote:
>>
>> What happens on real hardware when the BIOS boots and finds out that the
>> PCI hole is too small to contain all the MMIO regions of the PCI devices?
>>
>
> I do not know what does BIOS do details, but I think it's in 4G above if pci 
> hole is too small. I saw native OS program the pci hole to a very high addr 
> 0x3c0c00000000 if the pci device has large bar size.
>
> For Xen hvmloader, it already policy that is: if PCI hole is too small, 
> another MMIO region will be created starting from the high_mem_pgend.

Yes, and that, as I understand it, is the problem: that this change of
the MMIO regions is not communicated to qemu.

But it seems like this same problem would occur on real hardware --
i.e., you add a new video card with 2GiB of video ram, and now you
need a 2.5 GiB MMIO hole. It seems like the BIOS would be the logical
place to sort it out.  But I'm not familiar enough with SeaBIOS / qemu
to really know for sure.

 -George

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