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Fri, 25 Sep 2026 13:45:31 +0000 (GMT) Received: from [9.111.23.152] (unknown [9.111.23.152]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 25 Sep 2026 13:45:30 +0000 (GMT) Message-ID: <6ed30827-e79f-4fdb-8e26-dd14860f1d4f@linux.ibm.com> Date: Fri, 25 Sep 2026 15:45:30 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/3] KVM: s390: Improve floating IRQ injection behavior To: Christian Borntraeger , kvm@vger.kernel.org Cc: imbrenda@linux.ibm.com, linux-s390@vger.kernel.org, pasic@linux.ibm.com References: <20260820121546.24694-1-frankja@linux.ibm.com> <20260820121546.24694-2-frankja@linux.ibm.com> Content-Language: en-US From: Janosch Frank Autocrypt: addr=frankja@linux.ibm.com; keydata= xsFNBFubpD4BEADX0uhkRhkj2AVn7kI4IuPY3A8xKat0ihuPDXbynUC77mNox7yvK3X5QBO6 qLqYr+qrG3buymJJRD9xkp4mqgasHdB5WR9MhXWKH08EvtvAMkEJLnqxgbqf8td3pCQ2cEpv 15mH49iKSmlTcJ+PvJpGZcq/jE42u9/0YFHhozm8GfQdb9SOI/wBSsOqcXcLTUeAvbdqSBZe zuMRBivJQQI1esD9HuADmxdE7c4AeMlap9MvxvUtWk4ZJ/1Z3swMVCGzZb2Xg/9jZpLsyQzb lDbbTlEeyBACeED7DYLZI3d0SFKeJZ1SUyMmSOcr9zeSh4S4h4w8xgDDGmeDVygBQZa1HaoL Esb8Y4avOYIgYDhgkCh0nol7XQ5i/yKLtnNThubAcxNyryw1xSstnKlxPRoxtqTsxMAiSekk 0m3WJwvwd1s878HrQNK0orWd8BzzlSswzjNfQYLF466JOjHPWFOok9pzRs+ucrs6MUwDJj0S cITWU9Rxb04XyigY4XmZ8dywaxwi2ZVTEg+MD+sPmRrTw+5F+sU83cUstuymF3w1GmyofgsU Z+/ldjToHnq21MNa1wx0lCEipCCyE/8K9B9bg9pUwy5lfx7yORP3JuAUfCYb8DVSHWBPHKNj HTOLb2g2UT65AjZEQE95U2AY9iYm5usMqaWD39pAHfhC09/7NQARAQABzSVKYW5vc2NoIEZy YW5rIDxmcmFua2phQGxpbnV4LmlibS5jb20+wsF3BBMBCAAhBQJbm6Q+AhsjBQsJCAcCBhUI CQoLAgQWAgMBAh4BAheAAAoJEONU5rjiOLn4p9gQALjkdj5euJVI2nNT3/IAxAhQSmRhPEt0 AmnCYnuTcHRWPujNr5kqgtyER9+EMQ0ZkX44JU2q7OWxTdSNSAN/5Z7qmOR9JySvDOf4d3mS bMB5zxL9d8SbnSs1uW96H9ZBTlTQnmLfsiM9TetAjSrR8nUmjGhe2YUhJLR1v1LguME+YseT eXnLzIzqqpu311/eYiiIGcmaOjPCE+vFjcXL5oLnGUE73qSYiujwhfPCCUK0850o1fUAYq5p CNBCoKT4OddZR+0itKc/cT6NwEDwdokeg0+rAhxb4Rv5oFO70lziBplEjOxu3dqgIKbHbjza EXTb+mr7VI9O4tTdqrwJo2q9zLqqOfDBi7NDvZFLzaCewhbdEpDYVu6/WxprAY94hY3F4trT rQMHJKQENtF6ZTQc9fcT5I3gAmP+OEvDE5hcTALpWm6Z6SzxO7gEYCnF+qGXqp8sJVrweMub UscyLqHoqdZC2UG4LQ1OJ97nzDpIRe0g6oJ9ZIYHKmfw5jjwH6rASTld5MFWajWdNsqK15k/ RZnHAGICKVIBOBsq26m4EsBlfCdt3b/6emuBjUXR1pyjHMz2awWzCq6/6OWs5eANZ0sdosNq dq2v0ULYTazJz2rlCXV89qRa7ukkNwdBSZNEwsD4eEMicj1LSrqWDZMAALw50L4jxaMD7lPL jJbazsFNBFubpD4BEADAcUTRqXF/aY53OSH7IwIK9lFKxIm0IoFkOEh7LMfp7FGzaP7ANrZd cIzhZi38xyOkcaFY+npGEWvko7rlIAn0JpBO4x3hfhmhBD/WSY8LQIFQNNjEm3vzrMo7b9Jb JAqQxfbURY3Dql3GUzeWTG9uaJ00u+EEPlY8zcVShDltIl5PLih20e8xgTnNzx5c110lQSu0 iZv2lAE6DM+2bJQTsMSYiwKlwTuv9LI9Chnoo6+tsN55NqyMxYqJgElk3VzlTXSr3+rtSCwf tq2cinETbzxc1XuhIX6pu/aCGnNfuEkM34b7G1D6CPzDMqokNFbyoO6DQ1+fW6c5gctXg/lZ 602iEl4C4rgcr3+EpfoPUWzKeM8JXv5Kpq4YDxhvbitr8Dm8gr38+UKFZKlWLlwhQ56r/zAU v6LIsm11GmFs2/cmgD1bqBTNHHcTWwWtRTLgmnqJbVisMJuYJt4KNPqphTWsPY8SEtbufIlY HXOJ2lqUzOReTrie2u0qcSvGAbSfec9apTFl2Xko/ddqPcZMpKhBiXmY8tJzSPk3+G4tqur4 6TYAm5ouitJsgAR61Cu7s+PNuq/pTLDhK+6/Njmc94NGBcRA4qTuysEGE79vYWP2oIAU4Fv6 gqaWHZ4MEI2XTqH8wiwzPdCQPYsSE0fXWiYu7ObeErT6iLSTZGx4rQARAQABwsFfBBgBCAAJ BQJbm6Q+AhsMAAoJEONU5rjiOLn4DDEP/RuyckW65SZcPG4cMfNgWxZF8rVjeVl/9PBfy01K 8R0hajU40bWtXSMiby7j0/dMjz99jN6L+AJHJvrLz4qYRzn2Ys843W+RfXj62Zde4YNBE5SL jJweRCbMWKaJLj6499fctxTyeb9+AMLQS4yRSwHuAZLmAb5AyCW1gBcTWZb8ON5BmWnRqeGm IgC1EvCnHy++aBnHTn0m+zV89BhTLTUal35tcjUFwluBY39R2ux/HNlBO1GY3Z+WYXhBvq7q katThLjaQSmnOrMhzqYmdShP1leFTVbzXUUIYv/GbynO/YrL2gaQpaP1bEUEi8lUAfXJbEWG dnHFkciryi092E8/9j89DJg4mmZqOau7TtUxjRMlBcIliXkzSLUk+QvD4LK1kWievJse4mte FBdkWHfP4BH/+8DxapRcG1UAheSnSRQ5LiO50annOB7oXF+vgKIaie2TBfZxQNGAs3RQ+bga DchCqFm5adiSP5+OT4NjkKUeGpBe/aRyQSle/RropTgCi85pje/juYEn2P9UAgkfBJrOHvQ9 Z+2Sva8FRd61NJLkCJ4LFumRn9wQlX2icFbi8UDV3do0hXJRRYTWCxrHscMhkrFWLhYiPF4i phX7UNdOWBQ90qpHyAxHmDazdo27gEjfvsgYMdveKknEOTEb5phwxWgg7BcIDoJf9UMC In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: Q801NceOMG-cPQx7Bey1Jcz4wiCGMpfc X-Authority-Analysis: v=2.4 cv=EOCTQFZC c=1 sm=1 tr=0 ts=6ab67aff cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=VnNF1IyMAAAA:8 a=atEMzyAhulN_aJCjzi4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTI1MDA1NCBTYWx0ZWRfX+gtuJoAg9z/h tgkQj9NSX2mVdi+ORlAbEJ5opJBkolt5qrJt/TWzjPx4zTjJOYBSSLOkRyTrScEHQtZKf1v4gyj 3jzvs29AhChK92+fdX6+K2eQRVaCnRU= X-Proofpoint-GUID: Q801NceOMG-cPQx7Bey1Jcz4wiCGMpfc X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTI1MDA1NCBTYWx0ZWRfXwhjAnaGpXDWX /d+Ox1dfevSOvCXfltZiKgYoteot7jwgCNLZXEgB0OgargjwA4nB04WG81UUmuGY84+AoHY2fR6 /GRNcm8pqh/fCJf1ZbEa4ioPoBrKs/z2JXSbPRdNm2Afj1So+UPwEHd278OZJ7MOuncDv8SqPqV ZHxtwK0J1GQnQcTsY1xyyf5uKmTTDSGFR6EsS7AlD5ZP7mytGIduOdJk6EEz4jofawvuU56lv3L zEkB5c/LAr2sMyOgVH3e+5040NqTgQi55rXEsb8KTRvd617S9jjXl7Ec3SNRMgkAEHQ5pCtwM3H EcHrYGM93Zz+y9pt8nbEYTCzcphW6gVYwdwhtvrrLwUsmS2kseGY61DFgvU1uExr0+8oTAWin2y lbAbqjxinvT9ZBuUuHENo5vgPHbT1FfnZngCDJo959DQICnYoiA+0YYO5rR2gG6tXX/wuX5sr/5 H/9QnHG+VINBZZj/t7w== 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=2026-09-25_02,2026-09-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 phishscore=0 priorityscore=1501 clxscore=1015 spamscore=0 adultscore=0 impostorscore=0 lowpriorityscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609250054 On 9/25/26 11:26 AM, Christian Borntraeger wrote: > > > Am 20.08.26 um 14:12 schrieb Janosch Frank: >> Floating IRQs can be handled by any VCPU that opened its masks. The >> current design does not check if the mask is open when a floating IRQ >> is injected via the FLIC. It will wakeup the last VCPU that went >> sleeping hoping it's the correct one. >> >> Improve this by checking if the VCPU has pending IRQs and if not try > can deliver that particular IRQ> to find another VCPU which can take the IRQ. >> Ok >> This is not the final fix around this topic but we'll eventually >> inject a pending IRQ. The current code can easily deadlock a VM and >> with this fix we work around that. > > > One question below. > > > probably not the last version of that code ara but certainly a necessary > fix in the right direction. > > Acked-by: Christian Borntraeger > > We should apply this and add it to kvms390. We will get some > performance regression testing via the next kernel then and wait > for the results before sending out a pull request. Sure Knowing our own CI timeouts a change in either direction should be pretty obvious as well. > > >> [...] >> /* >> * Find a destination VCPU for a floating irq and kick it. >> */ >> -static void __floating_irq_kick(struct kvm *kvm, u64 type) >> +static void __floating_irq_kick(struct kvm *kvm, u64 type, int isc) >> { >> struct kvm_vcpu *dst_vcpu; >> int sigcpu, online_vcpus, nr_tries = 0; >> + u64 irq_pend_mask; >> + unsigned long i; >> >> online_vcpus = atomic_read(&kvm->online_vcpus); >> if (!online_vcpus) >> return; >> >> + irq_pend_mask = inti_to_irq_pend_mask(type, isc); >> for (sigcpu = kvm->arch.float_int.last_sleep_cpu; ; sigcpu++) { >> sigcpu %= online_vcpus; >> dst_vcpu = kvm_get_vcpu(kvm, sigcpu); >> - if (!is_vcpu_stopped(dst_vcpu)) >> + if (!is_vcpu_stopped(dst_vcpu) && >> + deliverable_irqs(dst_vcpu) & irq_pend_mask) >> break; >> /* avoid endless loops if all vcpus are stopped */ >> - if (nr_tries++ >= online_vcpus) >> - return; >> + if (nr_tries++ >= online_vcpus * 2) { > > why 2 rounds? I honestly can't recall why I can remove that change if you want.