Re: [Qemu-devel] how Windows treats BARs of driver-less devices when other devices are hotplugged

[Laszlo Ersek <lersek@redhat.com>]

On 02/25/16 15:18, Michael S. Tsirkin wrote:
> On Thu, Feb 25, 2016 at 03:05:08PM +0100, Laszlo Ersek wrote:
>> On 02/25/16 14:30, Michael S. Tsirkin wrote:

>>> virtio?
>>
>> ... was my first thought as well, but OVMF at the moment supports only
>> legacy (0.9.5) virtio-pci devices
> 
> Oh. We'll have to fix that too :(

Yes, there's a BZ open about it. It's very big work. Due to independent
reasons, I skimmed the virtio 1.0 spec the other day, specifically for
seeing what it would take to port the OVMF drivers forward to virtio
1.0. It's going to be a *lot* of work.

>> (and virtio-mmio only on AARCH64) --
>> those don't have MMIO BARs, only IO BARs.
> 
> Well that's not exactly true - there is an MSI-X BAR.
> Maybe OVMF does not enable that, though.

Correct.

The virtio stuff in OVMF adheres extremely closely to the 0.9.5 spec
(and the actual QEMU code was only studied when the guest wouldn't work
as described by the 0.9.5 spec -- this usually boiled down to silent
framing assumptions made by QEMU, and then the guest code was
accomodated), but the virtio code in OVMF is purposely absolutely
minimal, feature-wise.

I also looked up Gerd's virtio 1.0 patch series in the SeaBIOS git
history (from summer 2015, IIRC). It was extensive. Extrapolating from
that, you can imagine what it will take for OVMF.

Thanks
Laszlo