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Fri, 27 Aug 2021 14:06:19 +0000 (GMT) Received: from p-imbrenda (unknown [9.145.13.169]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id D1A6852063; Fri, 27 Aug 2021 14:06:18 +0000 (GMT) Date: Fri, 27 Aug 2021 16:06:16 +0200 From: Claudio Imbrenda To: Halil Pasic Cc: Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Heiko Carstens , Vasily Gorbik , kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Michael Mueller Subject: Re: [PATCH 1/1] KVM: s390: index kvm->arch.idle_mask by vcpu_idx Message-ID: <20210827160616.532d6699@p-imbrenda> In-Reply-To: <20210827125429.1912577-1-pasic@linux.ibm.com> References: <20210827125429.1912577-1-pasic@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: _9EcOdcMaTV3lvmIfWHyn5Wxy8xo9y3B X-Proofpoint-GUID: pZ2WiLbKyw6Jvb4Plinox0nbQh7DuH-W X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-08-27_04:2021-08-26,2021-08-27 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 phishscore=0 adultscore=0 malwarescore=0 lowpriorityscore=0 bulkscore=0 suspectscore=0 mlxlogscore=999 mlxscore=0 priorityscore=1501 impostorscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108270089 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 27 Aug 2021 14:54:29 +0200 Halil Pasic wrote: > While in practice vcpu->vcpu_idx == vcpu->vcp_id is often true, > it may not always be, and we must not rely on this. why? maybe add a simple explanation of why vcpu_idx and vcpu_id can be different, namely: KVM decides the vcpu_idx, userspace decides the vcpu_id, thus the two might not match > > Currently kvm->arch.idle_mask is indexed by vcpu_id, which implies > that code like > for_each_set_bit(vcpu_id, kvm->arch.idle_mask, online_vcpus) { > vcpu = kvm_get_vcpu(kvm, vcpu_id); you can also add a sentence to clarify that kvm_get_vcpu expects an vcpu_idx, not an vcpu_id. > do_stuff(vcpu); > } > is not legit. The trouble is, we do actually use kvm->arch.idle_mask > like this. To fix this problem we have two options. Either use > kvm_get_vcpu_by_id(vcpu_id), which would loop to find the right vcpu_id, > or switch to indexing via vcpu_idx. The latter is preferable for obvious > reasons. > > Let us make switch from indexing kvm->arch.idle_mask by vcpu_id to > indexing it by vcpu_idx. To keep gisa_int.kicked_mask indexed by the > same index as idle_mask lets make the same change for it as well. > > Signed-off-by: Halil Pasic > Fixes: 1ee0bc559dc3 ("KVM: s390: get rid of local_int array") otherwise looks good to me. Reviewed-by: Claudio Imbrenda > Cc: # 3.15+ > --- > arch/s390/include/asm/kvm_host.h | 1 + > arch/s390/kvm/interrupt.c | 12 ++++++------ > arch/s390/kvm/kvm-s390.c | 2 +- > arch/s390/kvm/kvm-s390.h | 2 +- > 4 files changed, 9 insertions(+), 8 deletions(-) > > diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h > index 161a9e12bfb8..630eab0fa176 100644 > --- a/arch/s390/include/asm/kvm_host.h > +++ b/arch/s390/include/asm/kvm_host.h > @@ -957,6 +957,7 @@ struct kvm_arch{ > atomic64_t cmma_dirty_pages; > /* subset of available cpu features enabled by user space */ > DECLARE_BITMAP(cpu_feat, KVM_S390_VM_CPU_FEAT_NR_BITS); > + /* indexed by vcpu_idx */ > DECLARE_BITMAP(idle_mask, KVM_MAX_VCPUS); > struct kvm_s390_gisa_interrupt gisa_int; > struct kvm_s390_pv pv; > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c > index d548d60caed2..16256e17a544 100644 > --- a/arch/s390/kvm/interrupt.c > +++ b/arch/s390/kvm/interrupt.c > @@ -419,13 +419,13 @@ static unsigned long deliverable_irqs(struct kvm_vcpu *vcpu) > static void __set_cpu_idle(struct kvm_vcpu *vcpu) > { > kvm_s390_set_cpuflags(vcpu, CPUSTAT_WAIT); > - set_bit(vcpu->vcpu_id, vcpu->kvm->arch.idle_mask); > + set_bit(kvm_vcpu_get_idx(vcpu), vcpu->kvm->arch.idle_mask); > } > > static void __unset_cpu_idle(struct kvm_vcpu *vcpu) > { > kvm_s390_clear_cpuflags(vcpu, CPUSTAT_WAIT); > - clear_bit(vcpu->vcpu_id, vcpu->kvm->arch.idle_mask); > + clear_bit(kvm_vcpu_get_idx(vcpu), vcpu->kvm->arch.idle_mask); > } > > static void __reset_intercept_indicators(struct kvm_vcpu *vcpu) > @@ -3050,18 +3050,18 @@ int kvm_s390_get_irq_state(struct kvm_vcpu *vcpu, __u8 __user *buf, int len) > > static void __airqs_kick_single_vcpu(struct kvm *kvm, u8 deliverable_mask) > { > - int vcpu_id, online_vcpus = atomic_read(&kvm->online_vcpus); > + int vcpu_idx, online_vcpus = atomic_read(&kvm->online_vcpus); > struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int; > struct kvm_vcpu *vcpu; > > - for_each_set_bit(vcpu_id, kvm->arch.idle_mask, online_vcpus) { > - vcpu = kvm_get_vcpu(kvm, vcpu_id); > + for_each_set_bit(vcpu_idx, kvm->arch.idle_mask, online_vcpus) { > + vcpu = kvm_get_vcpu(kvm, vcpu_idx); > if (psw_ioint_disabled(vcpu)) > continue; > deliverable_mask &= (u8)(vcpu->arch.sie_block->gcr[6] >> 24); > if (deliverable_mask) { > /* lately kicked but not yet running */ > - if (test_and_set_bit(vcpu_id, gi->kicked_mask)) > + if (test_and_set_bit(vcpu_idx, gi->kicked_mask)) > return; > kvm_s390_vcpu_wakeup(vcpu); > return; > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index 4527ac7b5961..8580543c5bc3 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -4044,7 +4044,7 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu) > kvm_s390_patch_guest_per_regs(vcpu); > } > > - clear_bit(vcpu->vcpu_id, vcpu->kvm->arch.gisa_int.kicked_mask); > + clear_bit(kvm_vcpu_get_idx(vcpu), vcpu->kvm->arch.gisa_int.kicked_mask); > > vcpu->arch.sie_block->icptcode = 0; > cpuflags = atomic_read(&vcpu->arch.sie_block->cpuflags); > diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h > index 9fad25109b0d..ecd741ee3276 100644 > --- a/arch/s390/kvm/kvm-s390.h > +++ b/arch/s390/kvm/kvm-s390.h > @@ -79,7 +79,7 @@ static inline int is_vcpu_stopped(struct kvm_vcpu *vcpu) > > static inline int is_vcpu_idle(struct kvm_vcpu *vcpu) > { > - return test_bit(vcpu->vcpu_id, vcpu->kvm->arch.idle_mask); > + return test_bit(kvm_vcpu_get_idx(vcpu), vcpu->kvm->arch.idle_mask); > } > > static inline int kvm_is_ucontrol(struct kvm *kvm) > > base-commit: 77dd11439b86e3f7990e4c0c9e0b67dca82750ba