From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH v9 21/22] KVM: s390: CPU model support for AP virtualization Date: Wed, 22 Aug 2018 18:57:31 +0200 Message-ID: References: <1534196899-16987-1-git-send-email-akrowiak@linux.vnet.ibm.com> <1534196899-16987-22-git-send-email-akrowiak@linux.vnet.ibm.com> <2c2c4859-ed3e-a492-dd59-78529c7768b2@redhat.com> <9f512d55-ef10-e2ae-f34e-e003c929bc3f@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <9f512d55-ef10-e2ae-f34e-e003c929bc3f@linux.ibm.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: pmorel@linux.ibm.com, Tony Krowiak , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: freude@de.ibm.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, borntraeger@de.ibm.com, cohuck@redhat.com, kwankhede@nvidia.com, bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com, alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com, alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com, thuth@redhat.com, pasic@linux.vnet.ibm.com, berrange@redhat.com, fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com, frankja@linux.ibm.com, Tony Krowiak List-ID: >>> >>> In this case we will have no problem with older guests not having idea >>> about APXA. >>> >>> Would it be a solution? >> >> Any feature the guest sees, should be part of the CPU model. The whole >> environment for cpu subfunctions is already in place both in KVM and >> QEMU. Only disabling subfunctions in KVM is not implemented yet. >> >> You can exclude any subfunctions/facilities that are only valid on LPAR >> level and cannot be used in some guest either way. (that makes life >> sometimes easier) >> >> >> I know that this might sound a little bit complicated, but it really >> isn't. Boils down to modifying kvm_s390_cpu_feat_init() and specifying >> some features+feature groups in QEMU. > > OK, we definitively need another patch/patch-set, to handle this. > Do you think it can be done in another series since if we always support > APXA when we have AP instructions, we already have an indication that > APXA exist: the AP facility. > Please implement the subfunction stuff right away. This will allow to handle all future facilities transparently from a kernel POV. Implementing that should be easy - and I don't like gluing features together in such a way. You can always assure that consistent data (e.g. AP + APXA availability) is reported from KVM to QEMU. > Regards, > Pierre > > > > -- Thanks, David / dhildenb