Re: [PULL 33/41] KVM: PPC: Book3S: Move KVM_REG_PPC_WORT to an unused register number

Alexander Graf
2014-05-30T15:58:15Z

On 30.05.14 17:55, Paolo Bonzini wrote:
> Il 30/05/2014 17:53, Alexander Graf ha scritto:
>>> This is an ABI break, this symbol was added in 3.14. I think I should
>>> revert this. Can you convince me otherwise?
>>
>> There's nothing bad happening with the change. Newer user space won't be
>> able to read WORT on older kernels, but there were more things broken
>> that just WORT for POWER8 support there ;).
>>
>> And user space build with new headers running on an old kernel won't
>> find the register, which is OK.
>
> Would new userspace with old kernel be able to detect that POWER8
> support isn't quite complete?

It couldn't, no. It would try to run a guest - if it happens to work
we're lucky ;). Even then the only thing that would remotely be affected
by that one_reg rename is live migration (which just got a few more
fixes in this pull request).

Alex