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Mon, 3 Aug 2026 15:03:16 +0000 (GMT) Date: Mon, 3 Aug 2026 17:03:14 +0200 From: Claudio Imbrenda To: Janosch Frank Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, borntraeger@de.ibm.com, david@kernel.org, seiden@linux.ibm.com, nrb@linux.ibm.com, schlameuss@linux.ibm.com, gra@linux.ibm.com Subject: Re: [PATCH v8 05/13] KVM: s390: ucontrol: Fix sca_clear_ext_call() Message-ID: <20260803170314.1a1f49b8@p-imbrenda> In-Reply-To: <8209fdba-9947-42e2-b124-81adf3419f15@linux.ibm.com> References: <20260803124040.126471-1-imbrenda@linux.ibm.com> <20260803124040.126471-6-imbrenda@linux.ibm.com> <8209fdba-9947-42e2-b124-81adf3419f15@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: cqSBz1j3zYXxzwUCVvqmvhnPA6imF1BU X-Proofpoint-Spam-Info: AW1haW4tMjYwODAzMDEzMyBTYWx0ZWRfX/okmUd1kWBhs KtXsdzaXW5Zevc81aFRK5HMzo4LX1YjlgeicJj0Glfa6tF4+eKxUxYtcmy5FjwhYjkQhoWpfYc/ CCGP3C6cn/V5tHO6vVSoNMB8wpGkLmE= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODAzMDEzMyBTYWx0ZWRfX4cmM4Vfhu2Ig buQkAW89THzHWdEAeWB00rQtg7PGJMhj7MwVzKJRBLhGrp4V/qXEI5k7q2e5O9TG3utdTbfFasq lazt9lz6e1R3eOPTC02F58ZCXoEfBhfCIEIjQHjIbgx1O+wyLADEjsYV1AO/Don3fFoWESQbVWQ 3IzPKn9s93aw7Gt4EnVjBUZN8Nz/FI1qdIFgOaAe8JGf3+wpZOqzVEKSvYFtm+BeIp4S21B9n0o yPBsKVTo2S+rKSu2eXFApFAcYAQdXANuPblzRH9nKk3klXV/cig4e/x+C+mqVbru2wfgWKaZkti ppA9E3NEh72LxJiaqcaWV03+EynuTaJaCANiSFtPe0/n6bjRChIHc/J7kk7eQrxSp7sZwjLJ0nQ oPAtcHsUkzPauIN8gMhEffoXVm2pQWNJ2VlsuKGA6tYYoCiz6Pz+rDfP7SE67H2vo8nv8NMX/ju EfNnLWNsyW0SQkR+hZw== X-Proofpoint-GUID: cqSBz1j3zYXxzwUCVvqmvhnPA6imF1BU X-Authority-Analysis: v=2.4 cv=KfzidwYD c=1 sm=1 tr=0 ts=6a70adbb cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=joHoxSTN3CKu4gl-UVAA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-03_03,2026-08-03_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 impostorscore=0 suspectscore=0 malwarescore=0 adultscore=0 clxscore=1015 priorityscore=1501 phishscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608030133 On Mon, 3 Aug 2026 16:50:30 +0200 Janosch Frank wrote: > On 8/3/26 14:40, Claudio Imbrenda wrote: > > When cleaning up a UCONTROL VM, sca_clear_ext_call() will touch memory > > outside of the allocated ESCA block, and UCONTROL VMs don't even use > > ESCA. > > > > Fix by not touching ESCA for UCONTROL VMs, and fence the > > KVM_S390_INTERRUPT ioctl altogether. Add extra checks in > > sca_ext_call_pending() and sca_inject_ext_call() to make sure UCONTROL > > VMs won't touch ESCA. > > > > Fencing does not cause regressions with userspace, since UCONTROL VMs > > never used KVM_S390_INTERRUPT ioctls. > > > > Signed-off-by: Claudio Imbrenda > > Fixes: 7d43bafcff17 ("KVM: s390: Make provisions for ESCA utilization") [...] > > @@ -84,10 +90,13 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id) > > static void sca_clear_ext_call(struct kvm_vcpu *vcpu) > > { > > struct esca_block *sca = vcpu->kvm->arch.sca; > > - union esca_sigp_ctrl *sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl; > > + union esca_sigp_ctrl *sigp_ctrl; > > > > - if (!kvm_s390_use_sca_entries() || !vcpu->arch.initialized) > > + if (!kvm_s390_use_sca_entries() || !vcpu->arch.initialized || kvm_is_ucontrol(vcpu->kvm)) > > return; > > + > > + /* Initialize after the above check, to prevent going out of bounds */ > > + sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl; > > Not sure why you only add this here and not at the other two occurences. because the other two were added later and I forgot about the comment :) > But I don't think we need these comments at all. > > Dereferencing things before a check is not a great idea in most cases. > Especially if the check validates if the memory has been set up at all :) > > > kvm_s390_clear_cpuflags(vcpu, CPUSTAT_ECALL_PEND); > > > > WRITE_ONCE(sigp_ctrl->value, 0); > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > > index 5b2727d7dfd1..21574f57be72 100644 > > --- a/arch/s390/kvm/kvm-s390.c > > +++ b/arch/s390/kvm/kvm-s390.c > > @@ -2934,6 +2934,9 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) > > case KVM_S390_INTERRUPT: { > > struct kvm_s390_interrupt s390int; > > > > + r = -EINVAL; > > + if (kvm_is_ucontrol(kvm)) > > + break; > > r = -EFAULT; > > if (copy_from_user(&s390int, argp, sizeof(s390int))) > > break; > > @@ -5456,6 +5459,8 @@ long kvm_arch_vcpu_unlocked_ioctl(struct file *filp, unsigned int ioctl, > > struct kvm_s390_interrupt s390int; > > struct kvm_s390_irq s390irq = {}; > > > > + if (kvm_is_ucontrol(vcpu->kvm)) > > + return -EINVAL; > > if (copy_from_user(&s390int, argp, sizeof(s390int))) > > return -EFAULT; > > if (s390int_to_s390irq(&s390int, &s390irq)) > > Do we need changes to the api documentation for this rc? The existing documentation is already not describing which error codes are possible and when.