On 25.01.2014, at 16:36, Victor Kamensky <victor.kamen...@linaro.org> wrote:

> On 25 January 2014 01:20, Alexander Graf <ag...@suse.de> wrote:
> 
>> It even
>> does it on BE PPC if you access devices through swizzling
>> buses, but we don't care as hypervisor. All we know in kvm is:
>> 
>>  - instruction used for access
>>  -> originating register (value)
>>  -> access size (len)
>>  -> virtual address (which we translate to phys)
>>  - guest endianness mode
> 
> Do you agree that in above if you just change guest endianness
> then device will see different (byteswapped) value so as far as
> device concerned it is completely different transactions, different
> effect. Why do we consider them? So if you want to see the
> same transaction and have the same effect on device, then when
> guest switches endianness it will need to add/drop byteswap,
> in order to have the same effect.

Yes. We consider it because KVM has to do the counter-swap manually based on 
the guest CPU's endianness setting because the only thing KVM knows are the 4 
bits I mentioned above.


Alex

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