linux-kernel - [PATCH] KVM: LAPIC: Narrow down the timer fastpath to tscdeadline timer

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Date:   Fri,  6 May 2022 02:47:37 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH] KVM: LAPIC: Narrow down the timer fastpath to tscdeadline timer

From: Wanpeng Li <wanpengli@...cent.com>

The original timer fastpath is developed for tscdeadline timer, however,
the apic timer periodic/oneshot mode which is emulated by vmx preemption
timer goes to preemption timer vmexit fastpath quietly, let's leave the 
complex recompute periodic timer's target expiration and restart apic 
timer to the slowpath vm-exit. Narrow down the timer fastpath to tscdeadline
timer mode.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kvm/lapic.c   |  6 ++++++
 arch/x86/kvm/lapic.h   |  1 +
 arch/x86/kvm/vmx/vmx.c | 14 +++++++++++---
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 137c3a2f5180..3e6cb2bf56dc 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2459,6 +2459,12 @@ static bool lapic_is_periodic(struct kvm_lapic *apic)
 	return apic_lvtt_period(apic);
 }
 
+bool lapic_is_tscdeadline(struct kvm_lapic *apic)
+{
+	return apic_lvtt_tscdeadline(apic);
+}
+EXPORT_SYMBOL_GPL(lapic_is_tscdeadline);
+
 int apic_has_pending_timer(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 4e4f8a22754f..6e1b2f349237 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -241,6 +241,7 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu);
 bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu);
 void kvm_lapic_restart_hv_timer(struct kvm_vcpu *vcpu);
 bool kvm_can_use_hv_timer(struct kvm_vcpu *vcpu);
+bool lapic_is_tscdeadline(struct kvm_lapic *apic);
 
 static inline enum lapic_mode kvm_apic_mode(u64 apic_base)
 {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index bb09fc9a7e55..2a8f4253df35 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5713,22 +5713,30 @@ static int handle_pml_full(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
-static fastpath_t handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
+static bool __handle_preemption_timer(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
 	if (!vmx->req_immediate_exit &&
 	    !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
 		kvm_lapic_expired_hv_timer(vcpu);
-		return EXIT_FASTPATH_REENTER_GUEST;
+		return true;
 	}
 
+	return false;
+}
+
+static fastpath_t handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
+{
+	if (lapic_is_tscdeadline(vcpu->arch.apic) && __handle_preemption_timer(vcpu))
+		return EXIT_FASTPATH_REENTER_GUEST;
+
 	return EXIT_FASTPATH_NONE;
 }
 
 static int handle_preemption_timer(struct kvm_vcpu *vcpu)
 {
-	handle_fastpath_preemption_timer(vcpu);
+	__handle_preemption_timer(vcpu);
 	return 1;
 }
 
-- 
2.25.1