KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer

stable inclusion
from stable-5.10.38
commit 2e0ce36d0bf695477f7ce42a0bb3ab09aee7c89c
bugzilla: 51875
CVE: NA

--------------------------------

[ Upstream commit d981dd15 ]

Commit ee66e453 (KVM: lapic: Busy wait for timer to expire when
using hv_timer) tries to set ktime->expired_tscdeadline by checking
ktime->hv_timer_in_use since lapic timer oneshot/periodic modes which
are emulated by vmx preemption timer also get advanced, they leverage
the same vmx preemption timer logic with tsc-deadline mode. However,
ktime->hv_timer_in_use is cleared before apic_timer_expired() handling,
let's delay this clearing in preemption-disabled region.

Fixes: ee66e453 ("KVM: lapic: Busy wait for timer to expire when using hv_timer")
Reviewed-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NWanpeng Li <wanpengli@tencent.com>
Message-Id: <1619608082-4187-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/x86/kvm/lapic.c

@@ -1908,8 +1908,8 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
 	if (!apic->lapic_timer.hv_timer_in_use)
 		goto out;
 	WARN_ON(rcuwait_active(&vcpu->wait));
-	cancel_hv_timer(apic);
 	apic_timer_expired(apic, false);
+	cancel_hv_timer(apic);
 
 	if (apic_lvtt_period(apic) && apic->lapic_timer.period) {
 		advance_periodic_target_expiration(apic);