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Wed, 1 Sep 2021 09:43:01 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E389CAE08F; Wed, 1 Sep 2021 09:43:00 +0000 (GMT) Received: from oc3016276355.ibm.com (unknown [9.145.181.78]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 1 Sep 2021 09:43:00 +0000 (GMT) Subject: Re: [PATCH v3 1/3] s390x: KVM: accept STSI for CPU topology information To: David Hildenbrand , kvm@vger.kernel.org Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, cohuck@redhat.com, thuth@redhat.com, imbrenda@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com References: <1627979206-32663-1-git-send-email-pmorel@linux.ibm.com> <1627979206-32663-2-git-send-email-pmorel@linux.ibm.com> From: Pierre Morel Message-ID: Date: Wed, 1 Sep 2021 11:43:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: fswuS0m00twXKBiHPvovRo4h9hOk-M50 X-Proofpoint-ORIG-GUID: -DYeszWcPdXR0QSo36MNC8OmjiSl-v02 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-09-01_03:2021-08-31,2021-09-01 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 spamscore=0 mlxscore=0 adultscore=0 bulkscore=0 phishscore=0 suspectscore=0 impostorscore=0 priorityscore=1501 malwarescore=0 lowpriorityscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2109010054 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/31/21 3:59 PM, David Hildenbrand wrote: > On 03.08.21 10:26, Pierre Morel wrote: >> STSI(15.1.x) gives information on the CPU configuration topology. >> Let's accept the interception of STSI with the function code 15 and >> let the userland part of the hypervisor handle it when userland >> support the CPU Topology facility. >> >> Signed-off-by: Pierre Morel >> --- >>   arch/s390/kvm/priv.c | 7 ++++++- >>   1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c >> index 9928f785c677..8581b6881212 100644 >> --- a/arch/s390/kvm/priv.c >> +++ b/arch/s390/kvm/priv.c >> @@ -856,7 +856,8 @@ static int handle_stsi(struct kvm_vcpu *vcpu) >>       if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE) >>           return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP); >> -    if (fc > 3) { >> +    if ((fc > 3 && fc != 15) || >> +        (fc == 15 && !test_kvm_facility(vcpu->kvm, 11))) { >>           kvm_s390_set_psw_cc(vcpu, 3); >>           return 0; >>       } >> @@ -893,6 +894,10 @@ static int handle_stsi(struct kvm_vcpu *vcpu) >>               goto out_no_data; >>           handle_stsi_3_2_2(vcpu, (void *) mem); >>           break; >> +    case 15: >> +        trace_kvm_s390_handle_stsi(vcpu, fc, sel1, sel2, operand2); >> +        insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2); >> +        return -EREMOTE; >>       } >>       if (kvm_s390_pv_cpu_is_protected(vcpu)) { >>           memcpy((void *)sida_origin(vcpu->arch.sie_block), (void *)mem, >> > > Sorry, I'm a bit rusty on s390x kvm facility handling. > > > For test_kvm_facility() to succeed, the facility has to be in both: > > a) fac_mask: actually available on the HW and supported by KVM > (kvm_s390_fac_base via FACILITIES_KVM, kvm_s390_fac_ext via > FACILITIES_KVM_CPUMODEL) > > b) fac_list: enabled for a VM > > AFAIU, facility 11 is neither in FACILITIES_KVM nor > FACILITIES_KVM_CPUMODEL, and I remember it's a hypervisor-managed bit. > > So unless we unlock facility 11 in FACILITIES_KVM_CPUMODEL, will > test_kvm_facility(vcpu->kvm, 11) ever successfully trigger here? > > > I'm pretty sure I am messing something up :) > I think it is the same remark that Christian did as wanted me to use the arch/s390/tools/gen_facilities.c to activate the facility. The point is that CONFIGURATION_TOPOLOGY, STFL, 11, is already defined inside QEMU since full_GEN10_GA1, so the test_kvm_facility() will succeed with the next patch setting the facility 11 in the mask when getting the KVM_CAP_S390_CPU_TOPOLOGY from userland. But if we activate it in KVM via any of the FACILITIES_KVM_xxx in the gen_facilities.c we will activate it for the guest what ever userland hypervizor we have, including old QEMU which will generate an exception. In this circumstances we have the choice between: - use FACILITY_KVM and handle everything in kernel - use FACILITY_KVM and use an extra CAPABILITY to handle part in kernel to avoid guest crash and part in userland - use only the extra CAPABILITY and handle almost everything in userland I want to avoid kernel code when not really necessary so I eliminated the first option. The last two are not very different but I found a better integration using the last one, allowing to use standard test_[kvm_]facility() Thanks for reviewing. Regards, Pierre -- Pierre Morel IBM Lab Boeblingen