Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6)

[Laszlo Ersek]

On 12/10/13 16:53, Gerd Hoffmann wrote:
> On Di, 2013-12-10 at 16:47 +0100, Laszlo Ersek wrote:
>> On 12/10/13 15:53, Gerd Hoffmann wrote:
>>>   Hi,
>>>
>>>> If we could make a small guset visible change, it would be simpler to
>>>> always make the PCI hole 1GB in size; it is currently 256MB for i440FX
>>>> and 1.25GB for q35.
>>>
>>> Easy for i440fx.
>>
>> I think it's going to break OVMF again.
> 
> Can't see a reason why it should.

PCI enumeration in OVMF assigns resources from a window that starts
exactly above the end of below-4gb-memory. For example, in case of a
2.5GB guest, the frame buffer bar of cirrus can be somewhere just above
2.5GB.

If you change the PCI hole in qemu so that it will start at 3GB, always,
then the ACPI tables exported by qemu will also advertise the big mmio
range starting at 3GB. OVMF will pass those tables through to the OS.
Accordingly, the OS will try to access the framebuffer above 3GB, but
OVMF has configured that bar between 2.5GB and 3GB.

IOW, I think this proposal would undo your [PATCH v2] piix: fix 32bit
pci hole.

I can of course live with whatever PCI hole as long as it is made
available to OVMF through an easy-to-parse fw_cfg file. Then I can sync
the OVMF enumeration to qemu's preference.

The fw_cfg file "etc/pci-info" allowed me to do exactly that. But it has
been killed. I'd like it to be resurrected, even if SeaBIOS ignores it.

Thanks,
Laszlo