On Wed, May 07 2014 at 10:42:54 am BST, Alexander Graf <agraf@xxxxxxx> wrote: >> 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. Huh? What if my guest has usespace using an idmap, with Stage-1 MMU for isolation only (much like an MPU)? R-class guests anyone? Agreed, this is not the general use case, but that doesn't seem to be completely unrealistic either. M. -- Jazz is not dead. It just smells funny. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html