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

Paolo Bonzini
2013-10-14T15:22:09Z

Il 14/10/2013 17:12, Marc Zyngier ha scritto:
> 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.

Devices are fine in QEMU, it's only the "generic" parts (rings) that are
missing AFAICT.

Paolo