KVM: X86: correct meaningless kvm_apicv_activated() check (8e205a6b) · Commits · 戴 / test

After test_and_set_bit() for kvm->arch.apicv_inhibit_reasons, we will always get false when calling kvm_apicv_activated() because it's sure apicv_inhibit_reasons do not equal to 0. What the code wants to do, is check whether APICv was *already* active and if so skip the costly request; we can do this using cmpxchg. Reported-by:

Miaohe Lin <linmiaohe@huawei.com> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

+16 −9

Original line number	Diff line number	Diff line
		@@ -8049,19 +8049,26 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_update_apicv);
		*/
		void kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit)
		{
		unsigned long old, new, expected;

		if (!kvm_x86_ops->check_apicv_inhibit_reasons \|\|
		!kvm_x86_ops->check_apicv_inhibit_reasons(bit))
		return;

		if (activate) {
		if (!test_and_clear_bit(bit, &kvm->arch.apicv_inhibit_reasons) \|\|
		!kvm_apicv_activated(kvm))
		return;
		} else {
		if (test_and_set_bit(bit, &kvm->arch.apicv_inhibit_reasons) \|\|
		kvm_apicv_activated(kvm))
		old = READ_ONCE(kvm->arch.apicv_inhibit_reasons);
		do {
		expected = new = old;
		if (activate)
		__clear_bit(bit, &new);
		else
		__set_bit(bit, &new);
		if (new == old)
		break;
		old = cmpxchg(&kvm->arch.apicv_inhibit_reasons, expected, new);
		} while (old != expected);

		if (!!old == !!new)
		return;
		}

		trace_kvm_apicv_update_request(activate, bit);
		if (kvm_x86_ops->pre_update_apicv_exec_ctrl)

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