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

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

Hollis Blanchard wrote:
>> btw, isn't passthrough better handled through the tlb?  i.e. actually 
>> let the guest access the specially-configured memory?  You can have qemu 
>> mmap /dev/mem and install it as a memslot, and things should work, no?  
>> (well, you might need to set some cachablility flag or other).
>>     
>
> Hmm, yes you're right. Of course, qemu offers greater flexibility than
> MMUs (which are limited to page-sized granularity, for example), so it
> might still be useful to have qemu intercede.
>
>   

With the endian-aware instructions that doesn't matter, since you set 
the endianness on a per-instruction granularity.  And with guest tlb 
controlled endianness, surely you get page granularity as well?


> Since we're defining a stable ABI, I'd rather have the information
> present than miss it in the future...
>
>   

So now the question is, do we see the need for qemu to intercept writes 
to pass-through devices?  IMO the answer is no.  If it doesn't 
understand anything about the device, it would be better off doing a 
real pass through.  If it does understand the device, it should know 
which endianness it likes.

-- 
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