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. 

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 | 100 ++++++++++++++++++++-------------------------------
 1 file changed, 39 insertions(+), 61 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e93e549..7663246 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);
 
@@ -1349,46 +1350,9 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
 
 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();
-       apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
-                   * APIC_BUS_CYCLE_NS * apic->divide_count;
-
-       if (!apic->lapic_timer.period)
-               return;
-       /*
-        * Do not allow the guest to program periodic timers with small
-        * interval, since the hrtimers are not throttled by the host
-        * scheduler.
-        */
-       if (apic_lvtt_period(apic)) {
-               s64 min_period = min_timer_period_us * 1000LL;
-
-               if (apic->lapic_timer.period < min_period) {
-                       pr_info_ratelimited(
-                           "kvm: vcpu %i: requested %lld ns "
-                           "lapic timer period limited to %lld ns\n",
-                           apic->vcpu->vcpu_id,
-                           apic->lapic_timer.period, min_period);
-                       apic->lapic_timer.period = min_period;
-               }
-       }
-
        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, "
-                  "expire @ 0x%016" PRIx64 ".\n", __func__,
-                  APIC_BUS_CYCLE_NS, ktime_to_ns(now),
-                  kvm_lapic_get_reg(apic, APIC_TMICT),
-                  apic->lapic_timer.period,
-                  ktime_to_ns(ktime_add_ns(now,
-                               apic->lapic_timer.period)));
+               apic->lapic_timer.target_expiration,
+               HRTIMER_MODE_ABS_PINNED);
 }
 
 static bool set_target_expiration(struct kvm_lapic *apic)
@@ -1453,22 +1417,12 @@ 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);
@@ -1477,7 +1431,8 @@ 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,
@@ -1485,14 +1440,29 @@ 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);
+       start_hv_timer(apic);
 }
 EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_hv_timer);
 
@@ -1509,7 +1479,10 @@ 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);
 
@@ -1517,9 +1490,11 @@ 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);
        }
@@ -2052,8 +2027,11 @@ 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);
        }
 }
-- 
1.9.1

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