KVM: LAPIC: Trace LAPIC timer expiration on every vmentry

In commit ec0671d5 ("KVM: LAPIC: Delay trace_kvm_wait_lapic_expire
tracepoint to after vmexit", 2019-06-04), trace_kvm_wait_lapic_expire
was moved after guest_exit_irqoff() because invoking tracepoints within
kvm_guest_enter/kvm_guest_exit caused a lockdep splat.

These days this is not necessary, because commit 87fa7f3e ("x86/kvm:
Move context tracking where it belongs", 2020-07-09) restricted
the RCU extended quiescent state to be closer to vmentry/vmexit.
Moving the tracepoint back to __kvm_wait_lapic_expire is more accurate,
because it will be reported even if vcpu_enter_guest causes multiple
vmentries via the IPI/Timer fast paths, and it allows the removal of
advance_expire_delta.
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1650961551-38390-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -1648,10 +1648,10 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
 	tsc_deadline = apic->lapic_timer.expired_tscdeadline;
 	apic->lapic_timer.expired_tscdeadline = 0;
 	guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());
-	apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline;
+	trace_kvm_wait_lapic_expire(vcpu->vcpu_id, guest_tsc - tsc_deadline);
 
 	if (lapic_timer_advance_dynamic) {
-		adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta);
+		adjust_lapic_timer_advance(vcpu, guest_tsc - tsc_deadline);
 		/*
 		 * If the timer fired early, reread the TSC to account for the
 		 * overhead of the above adjustment to avoid waiting longer

arch/x86/kvm/lapic.h

@@ -38,7 +38,6 @@ struct kvm_timer {
 	u64 tscdeadline;
 	u64 expired_tscdeadline;
 	u32 timer_advance_ns;
-	s64 advance_expire_delta;
 	atomic_t pending;			/* accumulated triggered timers */
 	bool hv_timer_in_use;
 };

arch/x86/kvm/x86.c

@@ -10310,14 +10310,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	 */
 	guest_timing_exit_irqoff();
 
-	if (lapic_in_kernel(vcpu)) {
-		s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
-		if (delta != S64_MIN) {
-			trace_kvm_wait_lapic_expire(vcpu->vcpu_id, delta);
-			vcpu->arch.apic->lapic_timer.advance_expire_delta = S64_MIN;
-		}
-	}
-
 	local_irq_enable();
 	preempt_enable();