On Wed, 07 May 2014 10:52:01 +0100 Marc Zyngier <[email protected]> wrote:
> On Wed, May 07 2014 at 10:34:30 am BST, Peter Maydell > <[email protected]> wrote: > > On 6 May 2014 19:38, Peter Maydell <[email protected]> wrote: > >> On 6 May 2014 18:25, Marc Zyngier <[email protected]> wrote: > >>> On Tue, May 06 2014 at 3:28:07 pm BST, Will Deacon <[email protected]> > >>> 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. > > On AArch32, we only have the CPSR.E bit to select the endiannes. Are we > going to simply explode if the access comes from userspace? > > On AArch64, we can either select the kernel endianness, or userspace > endianness. Are we going to go a different route just for the sake of > enforcing kernel access? > > I'm inclined to think of userspace access as a valid use case. > > M. All the fuzz is not really about enforcing kernel access... PPC also has a current endianness selector (MSR_LE) but it only makes sense if you are in the cpu context. Initial versions of the virtio biendian support for QEMU PPC64 used an arbitrary cpu: in this case, the only sensible thing to look at to support kernel based virtio is the interrupt endianness selector (LPCR_ILE), because if gives a safe hint of the kernel endianness. The patch set has evolved and now uses current_cpu at device reset time. As a consequence, we are not necessarily tied to the kernel LPCR_ILE selector I guess. Cheers. -- Gregory Kurz [email protected] [email protected] Software Engineer @ IBM/Meiosys http://www.ibm.com Tel +33 (0)562 165 496 "Anarchy is about taking complete responsibility for yourself." Alan Moore. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
