linux-kernel - Re: [PATCH] KVM: x86: Allocate/free user_return

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Message-ID: <aRGOu3eJoRnsaV+n@intel.com>
Date: Mon, 10 Nov 2025 15:05:31 +0800
From: Chao Gao <chao.gao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: Allocate/free user_return_msrs at kvm.ko
 (un)loading time

>-static int kvm_init_user_return_msrs(void)
>+static void kvm_destroy_user_return_msrs(void)
> {
>-	user_return_msrs = alloc_percpu(struct kvm_user_return_msrs);
>-	if (!user_return_msrs) {
>-		pr_err("failed to allocate percpu user_return_msrs\n");
>-		return -ENOMEM;
>-	}
>+	int cpu;
>+
>+	for_each_possible_cpu(cpu)
>+		WARN_ON_ONCE(per_cpu(user_return_msrs, cpu).registered);

Could this warning be triggered if the forced shutdown path didn't
unregister the user return callback (i.e., with the patch [*] applied),
and then vendor modules got unloaded immediately after the forced shutdown
(before the CPU exits to the userspace)?

[*]: https://lore.kernel.org/kvm/20251030191528.3380553-4-seanjc@google.com/