From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Date: Fri, 30 May 2014 16:08:34 +0000 Subject: Re: [PULL 33/41] KVM: PPC: Book3S: Move KVM_REG_PPC_WORT to an unused register number Message-Id: <5388AD02.8010304@suse.de> List-Id: 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> In-Reply-To: <5388ABBE.3000704@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Paolo Bonzini , kvm-ppc@vger.kernel.org Cc: kvm@vger.kernel.org, mtosatti@redhat.com, Paul Mackerras 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 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