Re: [Qemu-devel] [PATCH v3 3/4] target-ppc: ppc can be either endian

[Alexander Graf <agraf@suse.de>]

On 07.05.14 10:14, Greg Kurz wrote:
> On Tue, 6 May 2014 19:37:22 +0100
> Peter Maydell <peter.maydell@linaro.org> wrote:
>> On 5 May 2014 09:07, Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:
>>> POWER7, POWER7+ and POWER8 families use the ILE bit of the LPCR
>>> special purpose register to decide the endianness to use when
>>> entering interrupt handlers. When running a Linux guest, this
>>> provides a hint on the endianness used by the kernel. From a
>>> QEMU point of view, the information is needed for legacy virtio
>>> support and crash dump support as well.
>> Do you care about the case of:
>>   * kernel bigendian
> Yes. FWIW, ppc64 is still widely used in big endian mode we don't
> want to break.
>
>>   * userspace littleendian (or vice-versa)
> We don't care about userspace here. We assume that virtio structures are
> owned by the guest kernel.
>
>>   * guest kernel passes virtio device through to guest userspace
> Not sure to understand... could you please point me to an example ?
>
>>   * guest userspace is doing the manipulation of the device
>>
> Hmm... you mean we would have virtio drivers implemented in the guest
> userspace ? Does that exist ? Please elaborate.

Virtio bypasses the IOMMU by design, so user space drivers don't make 
sense here :).

I don't think we should overengineer hacks for legacy virtio.


Alex