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Re: [Qemu-devel] [PATCH v2] memory: Introduce DEVICE_HOST_ENDIAN for ram
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH v2] memory: Introduce DEVICE_HOST_ENDIAN for ram device |
Date: |
Tue, 28 Feb 2017 11:41:01 +1100 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
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 <address@hidden>
> Signed-off-by: Yongji Xie <address@hidden>
Reviewed-by: David Gibson <address@hidden>
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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