From: Wanpeng Li <wanpeng...@hotmail.com>

Most windows guests still utilize APIC Timer periodic/oneshot mode
instead of tsc-deadline mode, and the APIC Timer periodic/oneshot
mode are still emulated by high overhead hrtimer on host. This patch
converts the expected expire time of the periodic/oneshot mode to
guest deadline tsc in order to leverage VMX preemption timer logic
for APIC Timer tsc-deadline mode. After each preemption timer vmexit
preemption timer is restarted to emulate LVTT current-count register
is automatically reloaded from the initial-count register when the
count reaches 0. This patch reduces ~3800 cycles for each APIC Timer
periodic mode operation virtualization.

Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Radim Krčmář <rkrc...@redhat.com>
Cc: Yunhong Jiang <yunhong.ji...@intel.com>
Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
---
 arch/x86/kvm/lapic.c | 103 ++++++++++++++++++++++++++++++++++++---------------
 arch/x86/kvm/lapic.h |   1 +
 2 files changed, 75 insertions(+), 29 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0354a79..4e77d37 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1090,7 +1090,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
 
 static u32 apic_get_tmcct(struct kvm_lapic *apic)
 {
-       ktime_t remaining;
+       ktime_t remaining, now;
        s64 ns;
        u32 tmcct;
 
@@ -1101,7 +1101,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
                apic->lapic_timer.period == 0)
                return 0;
 
-       remaining = hrtimer_get_remaining(&apic->lapic_timer.timer);
+       now = apic->lapic_timer.timer.base->get_time();
+       remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
        if (ktime_to_ns(remaining) < 0)
                remaining = ktime_set(0, 0);
 
@@ -1351,13 +1352,28 @@ static void start_sw_period(struct kvm_lapic *apic)
 {
        ktime_t now;
 
-       /* lapic timer in oneshot or periodic mode */
+       now = apic->lapic_timer.timer.base->get_time();
+
+       if (likely(ktime_compare(apic->lapic_timer.target_expiration, now)))
+               hrtimer_start(&apic->lapic_timer.timer,
+                       apic->lapic_timer.target_expiration,
+                       HRTIMER_MODE_ABS_PINNED);
+       else
+               apic_timer_expired(apic);
+}
+
+static bool set_target_expiration(struct kvm_lapic *apic)
+{
+       ktime_t now;
+       u64 tscl = rdtsc();
+
        now = apic->lapic_timer.timer.base->get_time();
        apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
-                   * APIC_BUS_CYCLE_NS * apic->divide_count;
+               * APIC_BUS_CYCLE_NS * apic->divide_count;
 
        if (!apic->lapic_timer.period)
-               return;
+               return false;
+
        /*
         * Do not allow the guest to program periodic timers with small
         * interval, since the hrtimers are not throttled by the host
@@ -1376,10 +1392,6 @@ static void start_sw_period(struct kvm_lapic *apic)
                }
        }
 
-       hrtimer_start(&apic->lapic_timer.timer,
-                     ktime_add_ns(now, apic->lapic_timer.period),
-                     HRTIMER_MODE_ABS_PINNED);
-
        apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
                   PRIx64 ", "
                   "timer initial count 0x%x, period %lldns, "
@@ -1389,6 +1401,12 @@ static void start_sw_period(struct kvm_lapic *apic)
                   apic->lapic_timer.period,
                   ktime_to_ns(ktime_add_ns(now,
                                apic->lapic_timer.period)));
+
+       apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) +
+               nsec_to_cycles(apic->vcpu, apic->lapic_timer.period);
+       apic->lapic_timer.target_expiration = ktime_add_ns(now, 
apic->lapic_timer.period);
+
+       return true;
 }
 
 bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
@@ -1406,22 +1424,12 @@ static void cancel_hv_timer(struct kvm_lapic *apic)
        apic->lapic_timer.hv_timer_in_use = false;
 }
 
-void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
-{
-       struct kvm_lapic *apic = vcpu->arch.apic;
-
-       WARN_ON(!apic->lapic_timer.hv_timer_in_use);
-       WARN_ON(swait_active(&vcpu->wq));
-       cancel_hv_timer(apic);
-       apic_timer_expired(apic);
-}
-EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
-
 static bool start_hv_timer(struct kvm_lapic *apic)
 {
        u64 tscdeadline = apic->lapic_timer.tscdeadline;
 
-       if (atomic_read(&apic->lapic_timer.pending) ||
+       if ((atomic_read(&apic->lapic_timer.pending) &&
+               !apic_lvtt_period(apic)) ||
                kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) {
                if (apic->lapic_timer.hv_timer_in_use)
                        cancel_hv_timer(apic);
@@ -1430,7 +1438,8 @@ static bool start_hv_timer(struct kvm_lapic *apic)
                hrtimer_cancel(&apic->lapic_timer.timer);
 
                /* In case the sw timer triggered in the window */
-               if (atomic_read(&apic->lapic_timer.pending))
+               if (atomic_read(&apic->lapic_timer.pending) &&
+                       !apic_lvtt_period(apic))
                        cancel_hv_timer(apic);
        }
        trace_kvm_hv_timer_state(apic->vcpu->vcpu_id,
@@ -1438,14 +1447,42 @@ static bool start_hv_timer(struct kvm_lapic *apic)
        return apic->lapic_timer.hv_timer_in_use;
 }
 
+void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
+{
+       struct kvm_lapic *apic = vcpu->arch.apic;
+
+       WARN_ON(!apic->lapic_timer.hv_timer_in_use);
+       WARN_ON(swait_active(&vcpu->wq));
+       cancel_hv_timer(apic);
+       apic_timer_expired(apic);
+
+       if (apic_lvtt_period(apic) &&
+               set_target_expiration(apic) &&
+               !start_hv_timer(apic))
+               start_sw_period(apic);
+}
+EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer);
+
 void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu)
 {
        struct kvm_lapic *apic = vcpu->arch.apic;
 
        WARN_ON(apic->lapic_timer.hv_timer_in_use);
 
-       if (apic_lvtt_tscdeadline(apic))
-               start_hv_timer(apic);
+       if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
+               ktime_t remaining, now;
+               u64 tscl = rdtsc();
+
+               now = apic->lapic_timer.timer.base->get_time();
+               remaining = hrtimer_get_remaining(&apic->lapic_timer.timer);
+               if (ktime_to_ns(remaining) < 0)
+                       remaining = ktime_set(0, 0);
+
+               apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, 
tscl) +
+                       nsec_to_cycles(apic->vcpu, ktime_to_ns(remaining));
+               apic->lapic_timer.target_expiration = ktime_add_ns(now, 
ktime_to_ns(remaining));
+       }
+       start_hv_timer(apic);
 }
 EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_hv_timer);
 
@@ -1462,7 +1499,10 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu *vcpu)
        if (atomic_read(&apic->lapic_timer.pending))
                return;
 
-       start_sw_tscdeadline(apic);
+       if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
+               start_sw_period(apic);
+       else if (apic_lvtt_tscdeadline(apic))
+               start_sw_tscdeadline(apic);
 }
 EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_sw_timer);
 
@@ -1470,9 +1510,11 @@ static void start_apic_timer(struct kvm_lapic *apic)
 {
        atomic_set(&apic->lapic_timer.pending, 0);
 
-       if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic))
-               start_sw_period(apic);
-       else if (apic_lvtt_tscdeadline(apic)) {
+       if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) {
+               if (set_target_expiration(apic) &&
+                       !(kvm_x86_ops->set_hv_timer && start_hv_timer(apic)))
+                       start_sw_period(apic);
+       } else if (apic_lvtt_tscdeadline(apic)) {
                if (!(kvm_x86_ops->set_hv_timer && start_hv_timer(apic)))
                        start_sw_tscdeadline(apic);
        }
@@ -2005,8 +2047,11 @@ void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu)
 
        if (atomic_read(&apic->lapic_timer.pending) > 0) {
                kvm_apic_local_deliver(apic, APIC_LVTT);
-               if (apic_lvtt_tscdeadline(apic))
+               if (!(apic_lvtt_period(apic) &&
+                       kvm_lapic_hv_timer_in_use(vcpu))) {
                        apic->lapic_timer.tscdeadline = 0;
+                       apic->lapic_timer.target_expiration = ktime_set(0, 0);
+               }
                atomic_set(&apic->lapic_timer.pending, 0);
        }
 }
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 031db26..e0c8023 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -15,6 +15,7 @@
 struct kvm_timer {
        struct hrtimer timer;
        s64 period;                             /* unit: ns */
+       ktime_t target_expiration;
        u32 timer_mode;
        u32 timer_mode_mask;
        u64 tscdeadline;
-- 
1.9.1

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