From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Krowiak Subject: Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback Date: Mon, 11 Jun 2018 08:50:49 -0400 Message-ID: <4f5f17f1-48ab-6f1e-6ef2-3741fc39e5f4@linux.ibm.com> References: <1525705912-12815-1-git-send-email-akrowiak@linux.vnet.ibm.com> <1525705912-12815-12-git-send-email-akrowiak@linux.vnet.ibm.com> <98ea7ce2-2539-e2ff-4bb4-297e784d87bd@linux.ibm.com> <7bb480ac-5723-83ff-c797-53c1ab0458c1@linux.vnet.ibm.com> <93cd0f46-a410-51c8-00b9-810c1b3d3ae2@linux.ibm.com> <0f37dc39-7355-19e5-40c9-a02a1ea58c2d@linux.vnet.ibm.com> <736a1346-f81a-7f71-7d13-38729ff78e4f@linux.ibm.com> <8f68183d-8385-8025-1898-23cad604ae94@linux.vnet.ibm.com> <9e30c9b0-a04c-0c4e-9d3d-37e7a53a7f72@linux.ibm.com> <5f9c3f97-34e2-bf68-b8ca-ac9288ea5efa@linux.vnet.ibm.com> <010679ed-bd80-42f8-3f6f-e4dee10e82f5@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Halil Pasic , pmorel@linux.ibm.com, 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, Janosch Frank List-ID: On 06/11/2018 07:32 AM, Halil Pasic wrote: > > > On 06/11/2018 11:23 AM, Pierre Morel wrote: >> On 08/06/2018 23:59, Tony Krowiak wrote: >>> On 06/07/2018 01:15 PM, Pierre Morel wrote: >>>> >> >> ...snip... >> >>>>>> >>>>>>> >>>>>>> Why maintain a list of kvm_ap_matrix structures if we don't have >>>>>>> to; it is stored >>>>>>> with the mediated matrix device which is passed in to all of the >>>>>>> vfio_ap driver >>>>>>> callbacks. >>>>>> >>>>>> Because using the vm_list which is a static in kvm makes you >>>>>> stick inside the kvm code. >>> >>> I understand your point here, but even if we did maintain a list of >>> kvm_ap_matrix structures, >>> we still need the kvm code to configure the guest's CRYCB and >>> eventually ECA.28. There is >>> also code in kvm-ap.c that is called from KVM. >> >> The only code from kvm-ap which is called from KVM is temporary code >> waiting for Harald to offer the clean interface to AP instructions. >> >>> The idea behind kvm-ap.c is that all code >>> related to configuration of AP structures in KVM is in this one spot. >> >> This I understand, but the code can be in one spot inside VFIO_AP >> instead >> of inside KVM. >> Putting the code inside KVM induce dependencies between KVM and AP >> while the kvm/vfio interface allows to avoid this dependency. >> >> The purpose of VFIO_AP is to handle the CRYCB, all get/clear/set >> crycb masks >> functions should be in VFIO AP. >> >> If we use wrappers in KVM, since the CRYCB is an a SIE extension, >> it is legitimate, the KVM interface to the CRYCB should only >> handle bitmaps and be unaware of the vfio_ap internal structures. >> >> >> Another concern, the kvm_ap_validate_queue_sharing() should not be >> inside KVM because it is a decision of current VFIO_AP driver >> to not share the queues between guest of level 2. >> >> The Z architecture does not allow to share AP queues between >> guests of level 1 but we could re-engineer the AP bus and the ' >> VFIO AP to offer queue sharing for guest level 2. >> >> This would be a new VFIO_AP driver (and an AP bus extension). >> We should not have to change KVM for this. >> > > > Pierre's proposal makes a lot of sense to me. We would not need to take > the kvm_lock (which we need to traverse the vm_list safely) for the > validation, and we could have immediate validation (which is in my > opinion > better). > > Also your refcount (which is not a refcout) could go away. You simply > traverse your list and check for duplicates when hooking up the mdev > with KVM. > > And my opinion is if we don't have to add code to the kvm module we > better not. > > @Janosch: Does core KVM share my opinion? Okay, I'll make the change. > > > Regards, > Halil