linux-kernel - [PATCH RFC 4/7] KVM: timer: program timer to a dedicated CPU

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Date:   Fri,  8 Dec 2017 16:39:47 +0800
From:   Quan Xu <quan.xu0@...il.com>
To:     pbonzini@...hat.com, rkrcmar@...hat.com
Cc:     yang.zhang.wz@...il.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Luo <bn0418@...il.com>,
        Quan Xu <quan.xu0@...il.com>
Subject: [PATCH RFC 4/7] KVM: timer: program timer to a dedicated CPU

From: Ben Luo <bn0418@...il.com>

KVM always registers timer on the CPU which vCPU was running on.
Even though vCPU thread is rescheduled to another CPU, the timer
will be migrated to the target CPU as well. When timer expired,
timer interrupt could make guest-mode vCPU VM-exit on this CPU.

Since the working kthread scans periodically, some of the timer
events may be lost or delayed. We have to program these tsc-
deadline timestamps to MSR_IA32_TSC_DEADLINE as normal, which
will cause VM-exit and KVM will signal the working thread through
IPI to program timer, instread of registering on current CPU.

Signed-off-by: Yang Zhang <yang.zhang.wz@...il.com>
Signed-off-by: Quan Xu <quan.xu0@...il.com>
Signed-off-by: Ben Luo <bn0418@...il.com>
---
 arch/x86/kvm/lapic.c |    8 +++++++-
 arch/x86/kvm/x86.c   |    7 ++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 20a23bb..5835a27 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2072,7 +2072,13 @@ static enum hrtimer_restart apic_timer_fn(struct hrtimer *data)
 	struct kvm_timer *ktimer = container_of(data, struct kvm_timer, timer);
 	struct kvm_lapic *apic = container_of(ktimer, struct kvm_lapic, lapic_timer);
 
-	apic_timer_expired(apic);
+
+	if (pv_timer_enabled(apic->vcpu)) {
+		kvm_apic_local_deliver(apic, APIC_LVTT);
+		if (apic_lvtt_tscdeadline(apic))
+			apic->lapic_timer.tscdeadline = 0;
+	} else
+		apic_timer_expired(apic);
 
 	if (lapic_is_periodic(apic)) {
 		advance_periodic_target_expiration(apic);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5668774..3cbb223 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -26,6 +26,7 @@
 #include "tss.h"
 #include "kvm_cache_regs.h"
 #include "x86.h"
+#include "lapic.h"
 #include "cpuid.h"
 #include "pmu.h"
 #include "hyperv.h"
@@ -2196,7 +2197,11 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case APIC_BASE_MSR ... APIC_BASE_MSR + 0x3ff:
 		return kvm_x2apic_msr_write(vcpu, msr, data);
 	case MSR_IA32_TSCDEADLINE:
-		kvm_set_lapic_tscdeadline_msr(vcpu, data);
+		if (pv_timer_enabled(vcpu))
+			smp_call_function_single(PVTIMER_SYNC_CPU,
+					kvm_apic_sync_pv_timer, vcpu, 0);
+		else
+			kvm_set_lapic_tscdeadline_msr(vcpu, data);
 		break;
 	case MSR_IA32_TSC_ADJUST:
 		if (guest_cpuid_has(vcpu, X86_FEATURE_TSC_ADJUST)) {
-- 
1.7.1