Re: [Qemu-devel] [PATCH v2] memory: Introduce DEVICE_HOST_ENDIAN for ram device

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Feb 27, 2017 at 12:52:44PM +0800, Yongji Xie wrote:
> At the moment ram device's memory regions are DEVICE_NATIVE_ENDIAN. It's
> incorrect. This memory region is backed by a MMIO area in host, so the
> uint64_t data that MemoryRegionOps read from/write to this area should be
> host-endian rather than target-endian. Hence, current code does not work
> when target and host endianness are different which is the most common case
> on PPC64. To fix it, this introduces DEVICE_HOST_ENDIAN for the ram device.
> 
> This has been tested on PPC64 BE/LE host/guest in all possible combinations
> including TCG.
> 
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

The effect of the patch is certainly correct.  I remain a little
concerned that the name "host endian" might cause more confusion than
it resolves, but a better term isn't immediately obvious to me.

> ---
>  include/exec/cpu-common.h |    6 ++++++
>  memory.c                  |    2 +-
>  2 files changed, 7 insertions(+), 1 deletions(-)
> 
> diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
> index bd15853..eef74df 100644
> --- a/include/exec/cpu-common.h
> +++ b/include/exec/cpu-common.h
> @@ -36,6 +36,12 @@ enum device_endian {
>      DEVICE_LITTLE_ENDIAN,
>  };
>  
> +#if defined(HOST_WORDS_BIGENDIAN)
> +#define DEVICE_HOST_ENDIAN DEVICE_BIG_ENDIAN
> +#else
> +#define DEVICE_HOST_ENDIAN DEVICE_LITTLE_ENDIAN
> +#endif
> +
>  /* address in the RAM (different from a physical address) */
>  #if defined(CONFIG_XEN_BACKEND)
>  typedef uint64_t ram_addr_t;
> diff --git a/memory.c b/memory.c
> index ed8b5aa..17cfada 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1180,7 +1180,7 @@ static void memory_region_ram_device_write(void *opaque, hwaddr addr,
>  static const MemoryRegionOps ram_device_mem_ops = {
>      .read = memory_region_ram_device_read,
>      .write = memory_region_ram_device_write,
> -    .endianness = DEVICE_NATIVE_ENDIAN,
> +    .endianness = DEVICE_HOST_ENDIAN,
>      .valid = {
>          .min_access_size = 1,
>          .max_access_size = 8,

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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