[PATCH 4/7] KVM: lapic: Allow user to override auto-tuning of timer advancement

[Sean Christopherson <sean.j.christopherson@intel.com>]

Disable auto-tuning the timer advancement if the user specifies an
explicit value via the module param.  Aside from the obvious override
capability, this also allows the KVM admin to set the advancement
beyond the internally-capped max of 5000ns.

Cc: Wanpeng Li <wanpengli@tencent.com>
Fixes: 3b8a5df6c4dc6 ("KVM: LAPIC: Tune lapic_timer_advance_ns automatically")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/lapic.c | 2 ++
 arch/x86/kvm/lapic.h | 2 ++
 arch/x86/kvm/x86.c   | 2 +-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 70a0acd98e9e..c43cd26f040b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2286,6 +2286,8 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, u32 timer_advance_ns)
 		     HRTIMER_MODE_ABS_PINNED);
 	apic->lapic_timer.timer.function = apic_timer_fn;
 	apic->lapic_timer.timer_advance_ns = timer_advance_ns;
+	if (timer_advance_ns != LAPIC_TIMER_ADVANCE_DEFAULT_NS)
+		apic->lapic_timer.timer_advance_adjust_done = true;
 
 	/*
 	 * APIC is created enabled. This will prevent kvm_lapic_set_base from
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 3e97f8a68967..c7233629c05b 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -16,6 +16,8 @@
 #define APIC_BUS_CYCLE_NS       1
 #define APIC_BUS_FREQUENCY      (1000000000ULL / APIC_BUS_CYCLE_NS)
 
+#define LAPIC_TIMER_ADVANCE_DEFAULT_NS	1000
+
 enum lapic_mode {
 	LAPIC_MODE_DISABLED = 0,
 	LAPIC_MODE_INVALID = X2APIC_ENABLE,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b303a21a2bc2..709a8bf5ae0e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -137,7 +137,7 @@ static u32 __read_mostly tsc_tolerance_ppm = 250;
 module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
 
 /* lapic timer advance (tscdeadline mode only) in nanoseconds */
-static u32 __read_mostly lapic_timer_advance_ns = 1000;
+static u32 __read_mostly lapic_timer_advance_ns = LAPIC_TIMER_ADVANCE_DEFAULT_NS;
 module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR);
 
 static bool __read_mostly vector_hashing = true;
-- 
2.21.0