[PATCH RFC V3 3/6] KVM: LAPIC: introduce set_target_expiration() to set target expiration time

[Wanpeng Li <kernellwp@gmail.com>]

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

Introduce set_target_expiration() to set target expiration time which is 
when LVTT current-count register counts down to zero and a timer interrupt 
is generated.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Yunhong Jiang <yunhong.jiang@intel.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 arch/x86/kvm/lapic.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/lapic.h |  1 +
 2 files changed, 48 insertions(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index dce6c0b..09dad85 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1391,6 +1391,53 @@ static void start_sw_period(struct kvm_lapic *apic)
 				apic->lapic_timer.period)));
 }
 
+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;
+
+	if (!apic->lapic_timer.period)
+		return false;
+
+	/*
+	 * 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;
+		}
+	}
+
+	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.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)
 {
 	if (!lapic_in_kernel(vcpu))
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index f60d01c..889b504 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