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Wed, 22 Aug 2018 16:57:38 +0000 (UTC) Received: from [10.36.116.89] (ovpn-116-89.ams2.redhat.com [10.36.116.89]) by smtp.corp.redhat.com (Postfix) with ESMTP id 603652026D74; Wed, 22 Aug 2018 16:57:32 +0000 (UTC) Subject: Re: [PATCH v9 21/22] KVM: s390: CPU model support for AP virtualization 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 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> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <9f512d55-ef10-e2ae-f34e-e003c929bc3f@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Wed, 22 Aug 2018 16:57:38 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Wed, 22 Aug 2018 16:57:38 +0000 (UTC) for IP:'10.11.54.4' DOMAIN:'int-mx04.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'david@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> >>> 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