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

[Avi K. <av...@qu...>]

Hollis Blanchard wrote:
> 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.
>   

Okay, so it's at instruction granularity _and_ page granularity.  I'll 
apply that patch (with a #ifdef CONFIG_PPC so other archs don't use it 
by mistake).


-- 
error compiling committee.c: too many arguments to function