[PATCH v3 4/5] KVM: LAPIC: Delay trace advance expire delta

[Wanpeng Li]

From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

wait_lapic_expire() call was moved above guest_enter_irqoff() because of 
its tracepoint, which violated the RCU extended quiescent state invoked 
by guest_enter_irqoff()[1][2]. This patch simply moves the tracepoint 
below guest_exit_irqoff() in vcpu_enter_guest(). Snapshot the delta before 
VM-Enter, but trace it after VM-Exit. This can help us to move 
wait_lapic_expire() just before vmentry in the later patch.

[1] Commit 8b89fe1f6c43 ("kvm: x86: move tracepoints outside extended quiescent state")
[2] https://patchwork.kernel.org/patch/7821111/

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: Liran Alon <liran.alon@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
---
 arch/x86/kvm/lapic.c | 16 ++++++++--------
 arch/x86/kvm/lapic.h |  1 +
 arch/x86/kvm/x86.c   |  2 ++
 3 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 2f364fe..af38ece 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1502,27 +1502,27 @@ static inline void __wait_lapic_expire(struct kvm_vcpu *vcpu, u64 guest_cycles)
 }
 
 static inline void adaptive_tune_timer_advancement(struct kvm_vcpu *vcpu,
-				u64 guest_tsc, u64 tsc_deadline)
+				s64 advance_expire_delta)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
 	u64 ns;
 
 	/* too early */
-	if (guest_tsc < tsc_deadline) {
-		ns = (tsc_deadline - guest_tsc) * 1000000ULL;
+	if (advance_expire_delta < 0) {
+		ns = -advance_expire_delta * 1000000ULL;
 		do_div(ns, vcpu->arch.virtual_tsc_khz);
 		timer_advance_ns -= min((u32)ns,
 			timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
 	} else {
 	/* too late */
-		ns = (guest_tsc - tsc_deadline) * 1000000ULL;
+		ns = advance_expire_delta * 1000000ULL;
 		do_div(ns, vcpu->arch.virtual_tsc_khz);
 		timer_advance_ns += min((u32)ns,
 			timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
 	}
 
-	if (abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
+	if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
 		apic->lapic_timer.timer_advance_adjust_done = true;
 	if (unlikely(timer_advance_ns > 5000)) {
 		timer_advance_ns = 0;
@@ -1545,13 +1545,13 @@ void 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());
-	trace_kvm_wait_lapic_expire(vcpu->vcpu_id, guest_tsc - tsc_deadline);
+	apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline;
 
-	if (guest_tsc < tsc_deadline)
+	if (apic->lapic_timer.advance_expire_delta < 0)
 		__wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);
 
 	if (unlikely(!apic->lapic_timer.timer_advance_adjust_done))
-		adaptive_tune_timer_advancement(vcpu, guest_tsc, tsc_deadline);
+		adaptive_tune_timer_advancement(vcpu, apic->lapic_timer.advance_expire_delta);
 }
 
 static void start_sw_tscdeadline(struct kvm_lapic *apic)
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index d6d049b..3e72a25 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -32,6 +32,7 @@ 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;
 	bool timer_advance_adjust_done;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f2e3847..4a7b00c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7961,6 +7961,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	++vcpu->stat.exits;
 
 	guest_exit_irqoff();
+	trace_kvm_wait_lapic_expire(vcpu->vcpu_id,
+		vcpu->arch.apic->lapic_timer.advance_expire_delta);
 
 	local_irq_enable();
 	preempt_enable();
-- 
2.7.4