linux-kernel - Re: [RFC PATCH v3 5/7] KVM: x86: add vCPU scoped toggling for disabled exits

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Date:   Wed, 15 Jun 2022 10:43:16 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Kechen Lu <kechenl@...dia.com>
Cc:     kvm@...r.kernel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, somduttar@...dia.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 5/7] KVM: x86: add vCPU scoped toggling for
 disabled exits

>@@ -5980,6 +5987,8 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_event,
> int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> 			    struct kvm_enable_cap *cap)
> {
>+	struct kvm_vcpu *vcpu;
>+	unsigned long i;
> 	int r;
> 
> 	if (cap->flags)
>@@ -6036,14 +6045,17 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> 			break;
> 
> 		mutex_lock(&kvm->lock);
>-		if (kvm->created_vcpus)
>-			goto disable_exits_unlock;
>+		if (kvm->created_vcpus) {
>+			kvm_for_each_vcpu(i, vcpu, kvm) {
>+				kvm_ioctl_disable_exits(vcpu->arch, cap->args[0]);
>+				static_call(kvm_x86_update_disabled_exits)(vcpu);

IMO, this won't work on Intel platforms. Because, to manipulate a vCPU's
VMCS, vcpu_load() should be invoked in advance to load the VMCS.
Alternatively, you can add a request KVM_REQ_XXX and defer updating VMCS
to the next vCPU entry.

>+			}
>+		}
>+		mutex_unlock(&kvm->lock);
> 
> 		kvm_ioctl_disable_exits(kvm->arch, cap->args[0]);
> 
> 		r = 0;
>-disable_exits_unlock:
>-		mutex_unlock(&kvm->lock);
> 		break;
> 	case KVM_CAP_MSR_PLATFORM_INFO:
> 		kvm->arch.guest_can_read_msr_platform_info = cap->args[0];
>-- 
>2.32.0
>