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

Alexander Graf
2014-05-30T16:08:34Z

On 30.05.14 18:03, Paolo Bonzini wrote:
> Il 30/05/2014 17:58, Alexander Graf ha scritto:
>>>
>>> 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 ;).
>
> That's why I'm considering a revert.
>
>> 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).
>
> Doesn't "info cpus" also do get/set one_reg?

Yeah, but WORT is not important enough to get listed.

> What happens if it returns EINVAL? Also, reset should certainly try
> to write all registers, what happens if one is missed.

If it returns EINVAL we just ignore the register.

>
> Beyond the particular case of WORT, I'd just like to point out that
> uapi/ changes need even more scrutiny from maintainers than usual. I
> don't know exactly what checks Linus makes in my pull requests, but
> uapi/ is at the top of the list of things he might look at, right
> after the diffstat. :)

Consider that ONE_REG as experimental flagged :). Really, I am as
concerned as you are on ABI breakages, but in this case it's not worth
it. I'm not even sure any guest uses WORT at all. Linux doesn't seem to.

Alex