Re: [kvm-ppc-devel] RFC: MMIO endianness flag

[Hollis Blanchard <hollisb@us.ibm.com>]

On Thu, 2008-01-10 at 08:56 +0200, Avi Kivity wrote:
> 
> IIRC endianness is a per-page attribute on ppc, no?  Otherwise you'd 
> have a global attribute instead of per-access.

The MMU in some PowerPC can have per-page endianness, but not all. On a
processor that supports this attribute, I expect that when an MMIO trap
occurs we'll need to inspect the guest MMU state in order to set the
is_bigendian flag correctly.

The real issue I'm looking at right now is byte-reversed loads and
stores. For example, "lwzx" (Load Word and Zero Indexed) does a
big-endian 4-byte load, while "lwbrx" (Load Word Byte-Reverse Indexed)
does a little-endian 4-byte load. These instructions exist on all
PowerPC, and they can be issued at any time and do not depend on MMU
mappings.

-- 
Hollis Blanchard
IBM Linux Technology Center


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