From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pierre Morel Subject: Re: [PATCH v4 1/7] s390: ap: kvm: add PQAP interception for AQIC Date: Thu, 28 Feb 2019 14:16:09 +0100 Message-ID: References: <1550849400-27152-1-git-send-email-pmorel@linux.ibm.com> <1550849400-27152-2-git-send-email-pmorel@linux.ibm.com> <9f1d9241-39b9-adbc-d0e9-cb702e609cbc@linux.ibm.com> <4dc59125-7f96-cba8-651b-382ed8f8bff8@linux.ibm.com> <8526f468-9a4d-68d2-3868-0dad5ce16f46@linux.ibm.com> <6058a017-6404-af3c-62ef-2452214ac97c@de.ibm.com> <2391adc2-6611-034c-61c5-feb46e2a751b@de.ibm.com> <20190228122251.75b31f62.cohuck@redhat.com> Reply-To: pmorel@linux.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190228122251.75b31f62.cohuck@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Cornelia Huck , Christian Borntraeger Cc: Tony Krowiak , alex.williamson@redhat.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, frankja@linux.ibm.com, pasic@linux.ibm.com, david@redhat.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, freude@linux.ibm.com, mimu@linux.ibm.com List-ID: On 28/02/2019 12:22, Cornelia Huck wrote: > On Thu, 28 Feb 2019 12:03:38 +0100 > Christian Borntraeger wrote: > >> On 28.02.2019 10:42, Christian Borntraeger wrote: >> [...] >>>> Okay, let's go back to the genesis of this discussion; namely, my >>>> suggestion about moving the fc == 0x03 check into the hook code. If >>>> the vfio_ap module is not loaded, there will be no hook code. In that >>>> case, the check for the hook will fail and ultimately response code >>>> 0x01 will be set in the status word (which may not be the right thing >>>> to do?). You have not stated a single good reason for keeping this >>>> check, but I'm done with this silly argument. It certainly doesn't >>>> hurt anything. >>> >>> The instruction handler must handle the basic checks for the >>> instruction itself as outlined above. >>> >>> Do we want to allow QEMU to fully emulate everything (the ECA_APIE case being off)? >>> The we should pass along everything to QEMU, but this is already done with the >>> ECA_APIE check, correct? >>> >>> Do we agree that when we are beyond the ECA_APIE check, that we do not emulate >>> in QEMU and we have enabled the AP instructions interpretion? >>> If yes then this has some implication: >>> >>> 1. ECA is on and we should only get PQAP interception for specific FC (namely 3). >>> 2. What we certainly should check is the facility bit of the guest (65) and reject fc==3 >>> right away with a specification exception. I do not want the hook to mess with >>> the kvm cpu model. @Pierre would be good to actually check test_kvm_facility(vcpu->kvm, 65)) >>> 3. What shall we do when fc == 0x3? We can certainly do the check here OR in the >>> hook. As long as we have only fc==3 this does not matter. >>> >>> Correct? >> >> Thinking more about that, I think we should inject a specification exception for all >> unknown FCc != 0x3. That would also qualify for keeping it in the instruction handler. >> > > So, to summarize, the function should do: > - Is userspace supposed to emulate everything (!ECA_APIE)? Return > -EOPNOTSUPP to hand control to it. > - We are now interpreting the instruction in KVM. Do common checks > (PSTATE etc.) and inject exceptions, if needed. > - Now look at the fc; if there's a handler for it, call that; if not > (case does not attempt to call a specific handler, or no handler > registered), inject a specification exception. (Do we want pre-checks > like for facility 65 here, or in the handler?) > > That response code 0x01 thingy probably needs to go into the specific > handler function, if anywhere (don't know the semantics, sorry). What do you mean with specific handler function? If you mean a switch around the FC with static function's call, I agree, if you mean a jump into a hook I do not agree. > > Question: Will the handlers for the individual fcs need to generate > different exceptions on their own? I.e., do they need to do injections > themselves, or should the calling function possibly inject an exception > on error? There are some specificities. > > (Are there more possible fcs than 0x3 and whatever the other > subfunction was?) > Yes, at least 5 different FC are implemented in the Linux kernel today AFAIK. Regards, Pierre -- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany