Re: [PATCH v3] KVM: Specify byte order for KVM_EXIT_MMIO

[Christoffer Dall <christoffer.dall@linaro.org>]

On Tue, Jan 28, 2014 at 08:28:42AM -0800, Christoffer Dall wrote:
> The KVM API documentation is not clear about the semantics of the data
> field on the mmio struct on the kvm_run struct.
> 
> This has become problematic when supporting ARM guests on big-endian
> host systems with guests of both endianness types, because it is unclear
> how the data should be exported to user space.
> 
> This should not break with existing implementations as all supported
> existing implementations of known user space applications (QEMU and
> kvmtools for virtio) only support default endianness of the
> architectures on the host side.
> 
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Alexander Graf <agraf@suse.de>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> ---
> Changes [v2 - v3]:
>  - Change the semantics and wordings as per Scott's, Avi's, and Ben's
>    suggestions.
> 
> Changes [v1 - v2]:
>  - s/host kernel should/host user space should/
> 
>  Documentation/virtual/kvm/api.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 366bf4b..e11f09d 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -2565,6 +2565,10 @@ executed a memory-mapped I/O instruction which could not be satisfied
>  by kvm.  The 'data' member contains the written data if 'is_write' is
>  true, and should be filled by application code otherwise.
>  
> +The 'data' member contains, in its first 'len' bytes, the value as it would
> +appear if the VCPU performed a load or store of the appropriate width directly
> +to the byte array.
> +
>  NOTE: For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_DCR,
>        KVM_EXIT_PAPR and KVM_EXIT_EPR the corresponding
>  operations are complete (and guest state is consistent) only after userspace
> -- 
> 1.8.5.2
> 

Any more comments on this one, or can it be applied?

Thanks,
-- 
Christoffer