Re: [Qemu-devel] [PATCH 2/2] memory: fix the eventfd data endianness according to the host

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/03/2015 09:11, Greg Kurz wrote:
> The data argument is a host entity. It is not related to the target
> endianness. Let's introduce a HOST_WORDS_BIGENDIAN based helper for
> that.
> 
> This patch fixes ioeventfd and vhost for a ppc64le host running a ppc64le
> guest (only virtqueue 0 was handled, all others being byteswapped because
> of TARGET_WORDS_BIGENDIAN). It doesn't change functionnality for fixed
> endian architectures (i.e. doesn't break x86).
> 
> Reported-by: Cédric Le Goater <clg@fr.ibm.com>
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---
>  memory.c |   13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/memory.c b/memory.c
> index 6291cc0..1e29d40 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1549,6 +1549,15 @@ void memory_region_clear_flush_coalesced(MemoryRegion *mr)
>      }
>  }
>  
> +static bool eventfd_wrong_endianness(MemoryRegion *mr)
> +{
> +#ifdef HOST_WORDS_BIGENDIAN
> +    return mr->ops->endianness == DEVICE_LITTLE_ENDIAN;
> +#else
> +    return mr->ops->endianness == DEVICE_BIG_ENDIAN;
> +#endif
> +}
> +
>  void memory_region_add_eventfd(MemoryRegion *mr,
>                                 hwaddr addr,
>                                 unsigned size,
> @@ -1565,7 +1574,7 @@ void memory_region_add_eventfd(MemoryRegion *mr,
>      };
>      unsigned i;
>  
> -    adjust_endianness(&mrfd.data, size, memory_region_wrong_endianness(mr));
> +    adjust_endianness(&mrfd.data, size, eventfd_wrong_endianness(mr));

Strictly speaking, the place to do this would be kvm_set_ioeventfd_mmio.
 A hypothetical userspace ioeventfd emulation would not need the swap.

I can accept the patch, but it's better to add a comment.

Paolo

>      memory_region_transaction_begin();
>      for (i = 0; i < mr->ioeventfd_nb; ++i) {
>          if (memory_region_ioeventfd_before(mrfd, mr->ioeventfds[i])) {
> @@ -1598,7 +1607,7 @@ void memory_region_del_eventfd(MemoryRegion *mr,
>      };
>      unsigned i;
>  
> -    adjust_endianness(&mrfd.data, size, memory_region_wrong_endianness(mr));
> +    adjust_endianness(&mrfd.data, size, eventfd_wrong_endianness(mr));
>      memory_region_transaction_begin();
>      for (i = 0; i < mr->ioeventfd_nb; ++i) {
>          if (memory_region_ioeventfd_equal(mrfd, mr->ioeventfds[i])) {
>