From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [PULL 33/41] KVM: PPC: Book3S: Move KVM_REG_PPC_WORT to an unused register number Date: Fri, 30 May 2014 18:08:34 +0200 Message-ID: <5388AD02.8010304@suse.de> References: <1401453776-55285-1-git-send-email-agraf@suse.de> <1401453776-55285-34-git-send-email-agraf@suse.de> <5388A8DF.9050300@redhat.com> <5388A996.8010606@suse.de> <5388A9F6.5090301@redhat.com> <5388AA95.8050003@suse.de> <5388ABBE.3000704@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, mtosatti@redhat.com, Paul Mackerras To: Paolo Bonzini , kvm-ppc@vger.kernel.org Return-path: In-Reply-To: <5388ABBE.3000704@redhat.com> Sender: kvm-ppc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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