> Am 07.05.2014 um 11:34 schrieb Peter Maydell <peter.maydell@xxxxxxxxxx>:
>
>> On 6 May 2014 19:38, Peter Maydell <peter.maydell@xxxxxxxxxx> wrote:
>>> On 6 May 2014 18:25, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
>>>> On Tue, May 06 2014 at 3:28:07 pm BST, Will Deacon <will.deacon@xxxxxxx> wrote:
>>>>> On Thu, Apr 24, 2014 at 07:17:23PM +0100, Marc Zyngier wrote:
>>>>> + reg.addr = (u64)&data;
>>>>> + if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, ®) < 0)
>>>>> + die("KVM_GET_ONE_REG failed (SCTLR_EL1)");
>>>>> +
>>>>> + return (data & SCTLR_EL1_EE_MASK) ? VIRTIO_ENDIAN_BE : VIRTIO_ENDIAN_LE;
>>>>
>>>> This rules out guests where userspace and kernelspace can run with different
>>>> endinness. Whilst Linux doesn't currently do this, can we support it here?
>>>> It all gets a bit hairy if the guest is using a stage-1 SMMU to let
>>>> userspace play with a virtio device...
>>>
>>> Yeah, I suppose we could check either EE or E0 depending on the mode
>>> when the access was made. We already have all the information, just need
>>> to handle the case. I'll respin the series.
>
>> How virtio implementations should determine their endianness is
>> a spec question, I think; at any rate QEMU and kvmtool ought to
>> agree on how it's done. I think the most recent suggestion on the
>> QEMU mailing list (for PPC) is that we should care about the
>> guest kernel endianness, but I don't know if anybody thought of
>> the pass-through-to-userspace usecase...
>
> Current opinion on the qemu-devel thread seems to be that we
> should just define that the endianness of the virtio device is
> the endianness of the guest kernel at the point where the guest
> triggers a reset of the virtio device by writing zero the QueuePFN
> or Status registers.
Virtio by design has full access to guest physical memory. It doesn't route DMA via PCI. So user space drivers simply don't make sense here.
Alex
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