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Tue, 19 Oct 2021 21:35:25 +0000 (GMT) Received: from li-43c5434c-23b8-11b2-a85c-c4958fb47a68.ibm.com (unknown [9.171.54.36]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 19 Oct 2021 21:35:25 +0000 (GMT) Subject: Re: [PATCH 3/3] KVM: s390: clear kicked_mask if not idle after set To: Halil Pasic , Janosch Frank , Michael Mueller , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Cc: David Hildenbrand , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Pierre Morel , Tony Krowiak , Matthew Rosato , Niklas Schnelle , farman@linux.ibm.com, kvm@vger.kernel.org References: <20211019175401.3757927-1-pasic@linux.ibm.com> <20211019175401.3757927-4-pasic@linux.ibm.com> From: Christian Borntraeger Message-ID: Date: Tue, 19 Oct 2021 23:35:25 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20211019175401.3757927-4-pasic@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: LUQwbDoMta8hA603_k9IOvC67H3_vJmE X-Proofpoint-ORIG-GUID: gOziz8H_E1mXajVtH2CUjO_N1cLw1Y7x X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.182.1,Aquarius:18.0.790,Hydra:6.0.425,FMLib:17.0.607.475 definitions=2021-10-19_02,2021-10-19_01,2020-04-07_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 bulkscore=0 mlxlogscore=999 spamscore=0 malwarescore=0 phishscore=0 adultscore=0 clxscore=1015 impostorscore=0 priorityscore=1501 mlxscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109230001 definitions=main-2110190124 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 19.10.21 um 19:54 schrieb Halil Pasic: > The idea behind kicked mask is that we should not re-kick a vcpu > from __airqs_kick_single_vcpu() that is already in the middle of > being kicked by the same function. > > If however the vcpu that was idle before when the idle_mask was > examined, is not idle any more after the kicked_mask is set, that > means that we don't need to kick, and that we need to clear the > bit we just set because we may be beyond the point where it would > get cleared in the wake-up process. Since the time window is short, > this is probably more a theoretical than a practical thing: the race > window is small. > > To get things harmonized let us also move the clear from vcpu_pre_run() > to __unset_cpu_idle(). this part makes sense. > > Signed-off-by: Halil Pasic > Fixes: 9f30f6216378 ("KVM: s390: add gib_alert_irq_handler()") > --- > arch/s390/kvm/interrupt.c | 7 ++++++- > arch/s390/kvm/kvm-s390.c | 2 -- > 2 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c > index 2245f4b8d362..3c80a2237ef5 100644 > --- a/arch/s390/kvm/interrupt.c > +++ b/arch/s390/kvm/interrupt.c > @@ -426,6 +426,7 @@ static void __unset_cpu_idle(struct kvm_vcpu *vcpu) > { > kvm_s390_clear_cpuflags(vcpu, CPUSTAT_WAIT); > clear_bit(vcpu->vcpu_idx, vcpu->kvm->arch.idle_mask); > + clear_bit(vcpu->vcpu_idx, vcpu->kvm->arch.gisa_int.kicked_mask); > } > > static void __reset_intercept_indicators(struct kvm_vcpu *vcpu) > @@ -3064,7 +3065,11 @@ static void __airqs_kick_single_vcpu(struct kvm *kvm, u8 deliverable_mask) > /* lately kicked but not yet running */ > if (test_and_set_bit(vcpu_idx, gi->kicked_mask)) > return; > - kvm_s390_vcpu_wakeup(vcpu); > + /* if meanwhile not idle: clear and don't kick */ > + if (test_bit(vcpu_idx, kvm->arch.idle_mask)) > + kvm_s390_vcpu_wakeup(vcpu); > + else > + clear_bit(vcpu_idx, gi->kicked_mask); I think this is now a bug. We should not return but continue in that case, no? I think it might be safer to also clear kicked_mask in __set_cpu_idle From a CPUs perspective: We have been running and are on our way to become idle. There is no way that someone kicked us for a wakeup. In other words as long as we are running, there is no point in kicking us but when going idle we should get rid of old kick_mask bit. Doesnt this cover your scenario? > return; > } > } > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index 1c97493d21e1..6b779ef9f5fb 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -4067,8 +4067,6 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu) > kvm_s390_patch_guest_per_regs(vcpu); > } > > - clear_bit(vcpu->vcpu_idx, vcpu->kvm->arch.gisa_int.kicked_mask); > - > vcpu->arch.sie_block->icptcode = 0; > cpuflags = atomic_read(&vcpu->arch.sie_block->cpuflags); > VCPU_EVENT(vcpu, 6, "entering sie flags %x", cpuflags); >