Messages in this thread | | | Subject | Re: [PATCH v4 1/7] s390: ap: kvm: add PQAP interception for AQIC | From | Tony Krowiak <> | Date | Thu, 28 Feb 2019 10:45:49 -0500 |
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On 2/28/19 8:44 AM, Christian Borntraeger wrote: > > > On 28.02.2019 14:23, Pierre Morel wrote: >> On 28/02/2019 10:42, Christian Borntraeger wrote: >>> >>> >>> On 27.02.2019 19:00, Tony Krowiak wrote: >>>> On 2/27/19 3:09 AM, Pierre Morel wrote: >>>>> On 26/02/2019 16:47, Tony Krowiak wrote: >>>>>> On 2/26/19 6:47 AM, Pierre Morel wrote: >>>>>>> On 25/02/2019 19:36, Tony Krowiak wrote: >>>>>>>> On 2/22/19 10:29 AM, Pierre Morel wrote: >>>>>>>>> We prepare the interception of the PQAP/AQIC instruction for >>>>>>>>> the case the AQIC facility is enabled in the guest. >>>>>>>>> >>>>>>>>> We add a callback inside the KVM arch structure for s390 for >>>>>>>>> a VFIO driver to handle a specific response to the PQAP >>>>>>>>> instruction with the AQIC command. >>>>>>>>> >>>>>>>>> We inject the correct exceptions from inside KVM for the case the >>>>>>>>> callback is not initialized, which happens when the vfio_ap driver >>>>>>>>> is not loaded. >>>>>>>>> >>>>>>>>> If the callback has been setup we call it. >>>>>>>>> If not we setup an answer considering that no queue is available >>>>>>>>> for the guest when no callback has been setup. >>>>>>>>> >>>>>>>>> We do consider the responsability of the driver to always initialize >>>>>>>>> the PQAP callback if it defines queues by initializing the CRYCB for >>>>>>>>> a guest. >>>>>>>>> >>>>>>>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >>>>>>> >>>>>>> ...snip... >>>>>>> >>>>>>>>> @@ -592,6 +593,55 @@ static int handle_io_inst(struct kvm_vcpu *vcpu) >>>>>>>>> } >>>>>>>>> } >>>>>>>>> +/* >>>>>>>>> + * handle_pqap: Handling pqap interception >>>>>>>>> + * @vcpu: the vcpu having issue the pqap instruction >>>>>>>>> + * >>>>>>>>> + * We now support PQAP/AQIC instructions and we need to correctly >>>>>>>>> + * answer the guest even if no dedicated driver's hook is available. >>>>>>>>> + * >>>>>>>>> + * The intercepting code calls a dedicated callback for this instruction >>>>>>>>> + * if a driver did register one in the CRYPTO satellite of the >>>>>>>>> + * SIE block. >>>>>>>>> + * >>>>>>>>> + * For PQAP/AQIC instructions only, verify privilege and specifications. >>>>>>>>> + * >>>>>>>>> + * If no callback available, the queues are not available, return this to >>>>>>>>> + * the caller. >>>>>>>>> + * Else return the value returned by the callback. >>>>>>>>> + */ >>>>>>>>> +static int handle_pqap(struct kvm_vcpu *vcpu) >>>>>>>>> +{ >>>>>>>>> + uint8_t fc; >>>>>>>>> + struct ap_queue_status status = {}; >>>>>>>>> + >>>>>>>>> + /* Verify that the AP instruction are available */ >>>>>>>>> + if (!ap_instructions_available()) >>>>>>>>> + return -EOPNOTSUPP; >>>>>>>> >>>>>>>> How can the guest even execute an AP instruction if the AP instructions >>>>>>>> are not available? If the AP instructions are not available on the host, >>>>>>>> they will not be available on the guest (i.e., CPU model feature >>>>>>>> S390_FEAT_AP will not be set). I suppose it doesn't hurt to check this >>>>>>>> here given QEMU may not be the only client. >>>>>>>> >>>>>>>>> + /* Verify that the guest is allowed to use AP instructions */ >>>>>>>>> + if (!(vcpu->arch.sie_block->eca & ECA_APIE)) >>>>>>>>> + return -EOPNOTSUPP; >>>>>>>>> + /* Verify that the function code is AQIC */ >>>>>>>>> + fc = vcpu->run->s.regs.gprs[0] >> 24; >>>>>>>>> + if (fc != 0x03) >>>>>>>>> + return -EOPNOTSUPP; >>>>>>>> >>>>>>>> You must have missed my suggestion to move this to the >>>>>>>> vcpu->kvm->arch.crypto.pqap_hook(vcpu) in the following responses: >>>>>>> >>>>>>> Please consider what happen if the vfio_ap module is not loaded. >>>>>> >>>>>> I have considered it and even verified my expectations empirically. If >>>>>> the vfio_ap module is not loaded, you will not be able to create an mdev device. >>>>> >>>>> OK, now please consider that another userland tool, not QEMU uses KVM. >>>> >>>> What does that have to do with loading the vfio_ap module? Without the >>>> vfio_ap module, there will be no AP devices for the guest. What are you >>>> suggesting here? >>>> >>>>> >>>>>> If you don't have an mdev device, you will not be able to >>>>>> start a guest with a vfio-ap device. If you start a guest without a >>>>>> vfio-ap device, but enable AP instructions for the guest, there will be >>>>>> no AP devices attached to the guest. Without any AP devices attached, >>>>>> the PQAP(AQIC) instructions will not ever get executed. >>>>> >>>>> This is not right. The instruction will be executed, eventually, after decoding. >>>> >>>> Please explain why the PQAP(AQIC) instruction will be executed on a >>>> guest without any devices? Point me to the code in the AP bus where >>>> PQAP(AQIC) is executed without a queue? >>> >>> The host must be prepared to handle malicous and broken guests. So if >>> a guest does PQAP, we must handle that gracefully (e.g. by injecting an >>> exception) >>> >>>> >>>>> >>>>>> Even if for some >>>>>> unknown reason the PQAP(AQIC) instruction is executed - for some unknown >>>>>> reason, it will fail with response code 0x01, AP-queue number not valid. >>>>> >>>>> No, before accessing the AP-queue the instruction will be decoded and depending on the installed micro-code it will fail with >>>>> - OPERATION EXCEPTION if the micro-code is not installed >>>>> - PRIVILEDGE OPERATION if the instruction is issued from userland (programm state) >>>>> - SPECIFICATION exception if the instruction do not respect the usage specification >>>>> >>>>> then it will be interpreted by the microcode and access the queue and only then it will fail with RC 0x01, AP queue not valid. >>>>> >>>>> In the case of KVM, we intercept the instruction because it is issued by the guest and we set the AQIC facility on to force interception. >>>>> >>>>> KVM do for us all the decode steps I mention here above, if there is or not a pqap hook to be call to simulate the QP queue access. >>>>> >>>>> That done, the AP queue virtualisation can be called, this is done by calling the hook. >>>> >>>> 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)) >> >> >> Currently the check test_kvm_facility(vcpu->kvm, 65) is done in the instruction handler, what do you mean here? > > Found it. I think we should couple the check for 64 to fc==3. Otherwise both things are somewhat > disconnected when reviewing.
I think you meant facility bit 65.
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