Re: [PATCH 0/3] virtio-mmio: handle BE guests on LE hosts

Marc Zyngier
2013-10-14T15:12:21Z

On 14/10/13 15:56, Paolo Bonzini wrote:
> Il 14/10/2013 16:52, Marc Zyngier ha scritto:
>>>> Sure. And I imagine this traps back into the kernel to read some
>>>> register and find out what the endianness of the accessing CPU is?
>>>
>>> Not yet. To be exact, it does the below today. But all virtio device
>>> emulation is 100% guest endianness unaware. This helper is the only
>>> piece of code where it gets any idea what endianness the guest has. So
>>> by checking for references to it in the code you know where endianness
>>> is an issue. And that's only in the config space.
>>
>> Only config space? How do you deal with virtio ring descriptors, for
>> example?
>
> They also use guest endianness, but do not use virtio_is_big_endian()
> (yet?) so Alex missed them.

Yeah, I thought as much. There is a whole bunch of things that need byte
swapping, both at the virtio level itself, and at the device level as well.

Grep-ing for __u{16,32,64} through include/uapi/linux/virtio* shows the
extent of the disaster.

M.
--
Jazz is not dead. It just smells funny...