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Subject[PATCH 5/5] KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support
Date
From: Wanpeng Li <wanpeng.li@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 <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 | 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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