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Thu, 20 Nov 2025 11:02:49 +0000 (GMT) Message-ID: <2087b6b4-34b4-4509-9cae-bfe719d99992@linux.ibm.com> Date: Thu, 20 Nov 2025 12:02:49 +0100 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 10/11] KVM: s390: Add VSIE shadow configuration To: Christoph Schlameuss , kvm@vger.kernel.org Cc: linux-s390@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Claudio Imbrenda , Nico Boehr , David Hildenbrand , Sven Schnelle , Paolo Bonzini , Shuah Khan References: <20251110-vsieie-v2-0-9e53a3618c8c@linux.ibm.com> <20251110-vsieie-v2-10-9e53a3618c8c@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: <20251110-vsieie-v2-10-9e53a3618c8c@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=BanVE7t2 c=1 sm=1 tr=0 ts=691ef560 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=XD9FR2GFIzR7_RmDYLQA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMiBTYWx0ZWRfX7tOkxTLD53Ck 4LRJ1Tnypd9O7ALvHPp9KbXvQ2JvNKqM/uFibGNshES7YpZa1tbUOP69391lrD5J3JS4J4UwXHB RWJX1y2Grx0TyveGp9BHXWYXAQrDcIP0gs0wYvn9M2qXN5YUVPom8A1XI/zIPXMg2KtwloSKWko EGaMJph2T6QJpS19436KM25otGbC2LisX84pL7WAJYTH71utnitpO5qTAqID6QbdqxzpFgTnviv zs9n/bGJ01i7P7SUbrEV86P9wxj55q9B9RSJyb1/qvpeWmkfZhmej5KZ6xTdjZFRL8Qyhq/Rc87 chz9ehnBMYQzgedPGW+6YeMQS0WS+ok9hc3b3LOq+WRMpOzgoY23ymEROdF4gAE9SP6FJ8ILVct YX/FHHUibSU2q9Kw8SvQa6CIwpK+TA== X-Proofpoint-GUID: _O7NC9J12CxsETds7IDta9I4tySF3Jpc X-Proofpoint-ORIG-GUID: _O7NC9J12CxsETds7IDta9I4tySF3Jpc X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-20_03,2025-11-20_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 lowpriorityscore=0 suspectscore=0 spamscore=0 impostorscore=0 priorityscore=1501 clxscore=1015 phishscore=0 bulkscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511150032 On 11/10/25 18:16, Christoph Schlameuss wrote: > Introduce two new module parameters allowing to keep more shadow > structures > > * vsie_shadow_scb_max > Override the maximum number of VSIE control blocks / vsie_pages to > shadow in guest-1. KVM will use the maximum of the current number of > vCPUs and a maximum of 256 or this value if it is lower. > This is the number of guest-3 control blocks / CPUs to keep shadowed > to minimize the repeated shadowing effort. KVM will either use this value or the number of current VCPUs. Either way the number will be capped to 256. > > * vsie_shadow_sca_max > Override the maximum number of VSIE system control areas to > shadow in guest-1. KVM will use a minimum of the current number of > vCPUs and a maximum of 256 or this value if it is lower. > This is the number of guest-3 system control areas / VMs to keep > shadowed to minimize repeated shadowing effort. > > Signed-off-by: Christoph Schlameuss Except for the current implementation with arrays, nothing is limiting us from going over 256 in the future by changing the code. I'm not sure if I ever want to see such an environment in practice though. > arch/s390/kvm/vsie.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c > index b69ef763b55296875522f2e63169446b5e2d5053..cd114df5e119bd289d14037d1f1c5bfe148cf5c7 100644 > --- a/arch/s390/kvm/vsie.c > +++ b/arch/s390/kvm/vsie.c > @@ -98,9 +98,19 @@ struct vsie_sca { > struct vsie_page *pages[KVM_S390_MAX_VSIE_VCPUS]; > }; > > +/* maximum vsie shadow scb */ > +unsigned int vsie_shadow_scb_max; Don't we need to initialize the variables or mark them static so they are 0? > +module_param(vsie_shadow_scb_max, uint, 0644); > +MODULE_PARM_DESC(vsie_shadow_scb_max, "Maximum number of VSIE shadow control blocks to keep. Values smaller number vcpus uses number of vcpus; maximum 256"); > + > +/* maximum vsie shadow sca */ > +unsigned int vsie_shadow_sca_max; > +module_param(vsie_shadow_sca_max, uint, 0644); > +MODULE_PARM_DESC(vsie_shadow_sca_max, "Maximum number of VSIE shadow system control areas to keep. Values smaller number of vcpus uses number of vcpus; 0 to disable sca shadowing; maximum 256"); > + > static inline bool use_vsie_sigpif(struct kvm *kvm) > { > - return kvm->arch.use_vsie_sigpif; > + return kvm->arch.use_vsie_sigpif && vsie_shadow_sca_max; This functions as the enablement of vsie_sigpif? Is there a reason why we don't want this enabled per default? > } > > static inline bool use_vsie_sigpif_for(struct kvm *kvm, struct vsie_page *vsie_page) > @@ -907,7 +917,8 @@ static struct vsie_sca *get_vsie_sca(struct kvm_vcpu *vcpu, struct vsie_page *vs > * We want at least #online_vcpus shadows, so every VCPU can execute the > * VSIE in parallel. (Worst case all single core VMs.) > */ > - max_sca = MIN(atomic_read(&kvm->online_vcpus), KVM_S390_MAX_VSIE_VCPUS); > + max_sca = MIN(MAX(atomic_read(&kvm->online_vcpus), vsie_shadow_sca_max), > + KVM_S390_MAX_VSIE_VCPUS); > if (kvm->arch.vsie.sca_count < max_sca) { > BUILD_BUG_ON(sizeof(struct vsie_sca) > PAGE_SIZE); > sca_new = (void *)__get_free_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO); > @@ -1782,7 +1793,8 @@ static struct vsie_page *get_vsie_page(struct kvm_vcpu *vcpu, unsigned long addr > put_vsie_page(vsie_page); > } > > - max_vsie_page = MIN(atomic_read(&kvm->online_vcpus), KVM_S390_MAX_VSIE_VCPUS); > + max_vsie_page = MIN(MAX(atomic_read(&kvm->online_vcpus), vsie_shadow_scb_max), > + KVM_S390_MAX_VSIE_VCPUS); > > /* allocate new vsie_page - we will likely need it */ > if (addr || kvm->arch.vsie.page_count < max_vsie_page) { >