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Mon, 31 Jan 2022 11:54:04 +0000 (GMT) Received: from li-e979b1cc-23ba-11b2-a85c-dfd230f6cf82 (unknown [9.171.30.167]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with SMTP; Mon, 31 Jan 2022 11:54:03 +0000 (GMT) Date: Mon, 31 Jan 2022 12:53:37 +0100 From: Halil Pasic To: Petr =?UTF-8?B?VGVzYcWZw61r?= Cc: Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Michael Mueller , Halil Pasic Subject: Re: [PATCH 1/1] KVM: s390: index kvm->arch.idle_mask by vcpu_idx Message-ID: <20220131125337.05f73251.pasic@linux.ibm.com> In-Reply-To: <3ca4de98-8f4d-9937-923e-f8865c96f82c@suse.cz> References: <20210827125429.1912577-1-pasic@linux.ibm.com> <3ca4de98-8f4d-9937-923e-f8865c96f82c@suse.cz> Organization: IBM X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: DLJPiBPGkgXLP74QnMzf_7wRLvHMlYG0 X-Proofpoint-ORIG-GUID: fVGO_KlqpsYh9m2hCs-yqCkwDA-VKiGY X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.816,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2022-01-31_04,2022-01-28_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 impostorscore=0 mlxlogscore=999 clxscore=1011 bulkscore=0 priorityscore=1501 adultscore=0 spamscore=0 suspectscore=0 mlxscore=0 malwarescore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2201110000 definitions=main-2201310077 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 31 Jan 2022 11:13:18 +0100 Petr Tesařík wrote: > Hi Halil, > > Dne 27. 08. 21 v 14:54 Halil Pasic napsal(a): > > While in practice vcpu->vcpu_idx == vcpu->vcp_id is often true, > > it may not always be, and we must not rely on this. > > > > 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); > > 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. > > I'm just backporting this fix to SLES 12 SP5, and I've noticed that > there is still this code in __floating_irq_kick(): > > /* find idle VCPUs first, then round robin */ > sigcpu = find_first_bit(fi->idle_mask, online_vcpus); > /* ... round robin loop removed ... > dst_vcpu = kvm_get_vcpu(kvm, sigcpu); > > It seems to me that this does exactly the thing that is not legit, but > I'm no expert. Did I miss something? > We made that legit by making the N-th bit in idle_mask correspond to the vcpu whose vcpu_idx == N. The second argument of kvm_get_vcpu() is the vcpu_idx. IMHO that ain't super-intuitive because it ain't spelled out. So before this was a mismatch (with a vcpu_id based bitmap we would have to use kvm_get_vcpu_by_id()), and with this patch applied this code becomes legit because both idle_mask and kvm_get_vcpu() operate with vcpu_idx. Does that make sense? I'm sorry the commit message did not convey this clearly enough... Regards, Halil > Petr T > > > 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") > > 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