linux-kernel - Re: [PATCH v4 2/4] KVM: x86: Leave user-return notifier registered on reboot/shutdown

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Message-ID: <aPHU+RZKwCK0BK7t@intel.com>
Date: Fri, 17 Oct 2025 13:32:41 +0800
From: Chao Gao <chao.gao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, "Kirill A. Shutemov"
	<kas@...nel.org>, <kvm@...r.kernel.org>, <x86@...nel.org>,
	<linux-coco@...ts.linux.dev>, <linux-kernel@...r.kernel.org>, Yan Zhao
	<yan.y.zhao@...el.com>, Xiaoyao Li <xiaoyao.li@...el.com>, Rick Edgecombe
	<rick.p.edgecombe@...el.com>, Hou Wenlong <houwenlong.hwl@...group.com>
Subject: Re: [PATCH v4 2/4] KVM: x86: Leave user-return notifier registered
 on reboot/shutdown

> bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu)
>@@ -14363,6 +14377,11 @@ module_init(kvm_x86_init);
> 
> static void __exit kvm_x86_exit(void)
> {
>+	int cpu;
>+
>+	for_each_possible_cpu(cpu)
>+		WARN_ON_ONCE(per_cpu_ptr(user_return_msrs, cpu)->registered);

Is it OK to reference user_return_msrs during kvm.ko unloading? IIUC,
user_return_msrs has already been freed during kvm-{intel,amd}.ko unloading.
See:

vmx_exit/svm_exit()
  -> kvm_x86_vendor_exit()
       -> free_percpu(user_return_msrs);

>+
>t 	WARN_ON_ONCE(static_branch_unlikely(&kvm_has_noapic_vcpu));
> }
> module_exit(kvm_x86_exit);
>-- 
>2.51.0.858.gf9c4a03a3a-goog
>
>