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The difference compared to the kvm_setup_empty_irq_routing() is this function just alloc the empty irq routing and does not need synchronize srcu, as we will call it in kvm_create_vm(). This patch is a preparatory step for an upcoming patch to avoid delay in KVM_CAP_SPLIT_IRQCHIP ioctl. Signed-off-by: Yi Wang --- include/linux/kvm_host.h | 1 + virt/kvm/irqchip.c | 19 +++++++++++++++++++ 2 files changed, 20 insertions(+) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 4944136efaa2..e91525c0a4ea 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -2000,6 +2000,7 @@ int kvm_set_irq_routing(struct kvm *kvm, const struct kvm_irq_routing_entry *entries, unsigned nr, unsigned flags); +int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm); int kvm_set_routing_entry(struct kvm *kvm, struct kvm_kernel_irq_routing_entry *e, const struct kvm_irq_routing_entry *ue); diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c index 1e567d1f6d3d..90fc43bd0fe4 100644 --- a/virt/kvm/irqchip.c +++ b/virt/kvm/irqchip.c @@ -237,3 +237,22 @@ int kvm_set_irq_routing(struct kvm *kvm, =20 return r; } + +int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm) +{ + struct kvm_irq_routing_table *new; + u32 i, j; + + new =3D kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT); 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charset="utf-8" Setup empty irq routing when kvm_create_vm(), so that x86 and s390 no longer need to set empty/dummy irq routing when creating an IRQCHIP 'cause it avoid an synchronize_srcu. Signed-off-by: Yi Wang --- virt/kvm/kvm_main.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7db96875ac46..db1b13fc0502 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1242,6 +1242,10 @@ static struct kvm *kvm_create_vm(unsigned long type,= const char *fdname) if (r) goto out_err; =20 + r =3D kvm_setup_empty_irq_routing_lockless(kvm); + if (r) + goto out_err; + mutex_lock(&kvm_lock); list_add(&kvm->vm_list, &vm_list); mutex_unlock(&kvm_lock); --=20 2.39.3 From nobody Thu Dec 25 08:56:19 2025 Received: from mail-pl1-f175.google.com (mail-pl1-f175.google.com [209.85.214.175]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 34852374F9; Sun, 21 Jan 2024 11:18:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.175 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; 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Sun, 21 Jan 2024 03:18:14 -0800 (PST) Received: from localhost.localdomain ([43.132.141.9]) by smtp.gmail.com with ESMTPSA id jc9-20020a17090325c900b001d7233f1a92sm3560255plb.221.2024.01.21.03.18.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 Jan 2024 03:18:14 -0800 (PST) From: Yi Wang X-Google-Original-From: Yi Wang To: seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, wanpengli@tencent.com, foxywang@tencent.com, oliver.upton@linux.dev, maz@kernel.org, anup@brainfault.org, atishp@atishpatra.org, borntraeger@linux.ibm.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com Cc: up2wing@gmail.com Subject: [v2 3/4] KVM: x86: don't setup empty irq routing when KVM_CAP_SPLIT_IRQCHIP Date: Sun, 21 Jan 2024 19:17:29 +0800 Message-Id: <20240121111730.262429-4-foxywang@tencent.com> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20240121111730.262429-1-foxywang@tencent.com> References: <20240121111730.262429-1-foxywang@tencent.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" We found that it may cost more than 20 milliseconds very accidentally to enable cap of KVM_CAP_SPLIT_IRQCHIP on a host which has many vms already. The reason is that when vmm(qemu/CloudHypervisor) invokes KVM_CAP_SPLIT_IRQCHIP kvm will call synchronize_srcu_expedited() and might_sleep and kworker of srcu may cost some delay during this period. As we have set up empty irq routing when creating vm, so this is no need now. Signed-off-by: Yi Wang --- arch/x86/kvm/irq.h | 1 - arch/x86/kvm/irq_comm.c | 5 ----- arch/x86/kvm/x86.c | 3 --- 3 files changed, 9 deletions(-) diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h index c2d7cfe82d00..76d46b2f41dd 100644 --- a/arch/x86/kvm/irq.h +++ b/arch/x86/kvm/irq.h @@ -106,7 +106,6 @@ void __kvm_migrate_timers(struct kvm_vcpu *vcpu); int apic_has_pending_timer(struct kvm_vcpu *vcpu); =20 int kvm_setup_default_irq_routing(struct kvm *kvm); -int kvm_setup_empty_irq_routing(struct kvm *kvm); int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src, struct kvm_lapic_irq *irq, struct dest_map *dest_map); diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c index 16d076a1b91a..99bf53b94175 100644 --- a/arch/x86/kvm/irq_comm.c +++ b/arch/x86/kvm/irq_comm.c @@ -392,11 +392,6 @@ int kvm_setup_default_irq_routing(struct kvm *kvm) =20 static const struct kvm_irq_routing_entry empty_routing[] =3D {}; =20 -int kvm_setup_empty_irq_routing(struct kvm *kvm) -{ - return kvm_set_irq_routing(kvm, empty_routing, 0, 0); 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Sun, 21 Jan 2024 03:18:18 -0800 (PST) Received: from localhost.localdomain ([43.132.141.9]) by smtp.gmail.com with ESMTPSA id jc9-20020a17090325c900b001d7233f1a92sm3560255plb.221.2024.01.21.03.18.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 Jan 2024 03:18:18 -0800 (PST) From: Yi Wang X-Google-Original-From: Yi Wang To: seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, wanpengli@tencent.com, foxywang@tencent.com, oliver.upton@linux.dev, maz@kernel.org, anup@brainfault.org, atishp@atishpatra.org, borntraeger@linux.ibm.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com Cc: up2wing@gmail.com Subject: [v2 4/4] KVM: s390: don't setup dummy routing when KVM_CREATE_IRQCHIP Date: Sun, 21 Jan 2024 19:17:30 +0800 Message-Id: <20240121111730.262429-5-foxywang@tencent.com> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20240121111730.262429-1-foxywang@tencent.com> References: <20240121111730.262429-1-foxywang@tencent.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" As we have setup empty irq routing in kvm_create_vm(), there's no need to setup dummy routing when KVM_CREATE_IRQCHIP. Signed-off-by: Yi Wang --- arch/s390/kvm/kvm-s390.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index acc81ca6492e..7c836c973b75 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -2999,14 +2999,11 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned i= nt ioctl, unsigned long arg) break; } case KVM_CREATE_IRQCHIP: { - struct kvm_irq_routing_entry routing; - - r =3D -EINVAL; - if (kvm->arch.use_irqchip) { - /* Set up dummy routing. */ - memset(&routing, 0, sizeof(routing)); - r =3D kvm_set_irq_routing(kvm, &routing, 0, 0); - } + /* + * As we have set up empty routing, there is no need to + * setup dummy routing here. + */ + r =3D 0; break; } case KVM_SET_DEVICE_ATTR: { --=20 2.39.3