[RFC PATCH 2/5] Utilize the vmx preemption timer

[Yunhong Jiang <yunhong.jiang@xxxxxxxxxxxxxxx>]

From: Yunhong Jiang <yunhong.jiang@xxxxxxxxx>

Adding the basic VMX preemption timer functionality, including checking
if the feature is supported, setup/clean the VMX preemption timer. Also
adds a parameter to state if the VMX preemption timer should be utilized.

Signed-off-by: Yunhong Jiang <yunhong.jiang@xxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  4 ++++
 arch/x86/kvm/lapic.c            |  7 +++++++
 arch/x86/kvm/vmx.c              | 45 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5e6b3ce7748f..8e58db20b3a4 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1006,6 +1006,10 @@ struct kvm_x86_ops {
 	int (*update_pi_irte)(struct kvm *kvm, unsigned int host_irq,
 			      uint32_t guest_irq, bool set);
 	void (*apicv_post_state_restore)(struct kvm_vcpu *vcpu);
+
+	int (*hw_emul_timer)(struct kvm_vcpu *vcpu);
+	void (*set_hwemul_timer)(struct kvm_vcpu *vcpu, u64 tsc);
+	void (*clear_hwemul_timer)(struct kvm_vcpu *vcpu);
 };
 
 struct kvm_arch_async_pf {
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index bbb5b283ff63..8908ee514f6c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -256,6 +256,13 @@ static inline int apic_lvtt_tscdeadline(struct kvm_lapic *apic)
 	return apic->lapic_timer.timer_mode == APIC_LVT_TIMER_TSCDEADLINE;
 }
 
+static inline int hw_emul_timer(struct kvm_lapic *apic)
+{
+	if (kvm_x86_ops->hw_emul_timer)
+		return kvm_x86_ops->hw_emul_timer(apic->vcpu);
+	return 0;
+}
+
 static inline int apic_lvt_nmi_mode(u32 lvt_val)
 {
 	return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9e078ff29f86..5475a7699ee5 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -110,6 +110,9 @@ module_param_named(pml, enable_pml, bool, S_IRUGO);
 
 #define KVM_VMX_TSC_MULTIPLIER_MAX     0xffffffffffffffffULL
 
+static bool __read_mostly hwemul_timer;
+module_param_named(hwemul_timer, hwemul_timer, bool, S_IRUGO);
+
 #define KVM_GUEST_CR0_MASK (X86_CR0_NW | X86_CR0_CD)
 #define KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST (X86_CR0_WP | X86_CR0_NE)
 #define KVM_VM_CR0_ALWAYS_ON						\
@@ -1056,6 +1059,20 @@ static inline bool cpu_has_vmx_virtual_intr_delivery(void)
 		SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY;
 }
 
+static inline bool cpu_has_preemption_timer(void)
+{
+	return vmcs_config.pin_based_exec_ctrl &
+		PIN_BASED_VMX_PREEMPTION_TIMER;
+}
+
+static inline int cpu_preemption_timer_multi(void)
+{
+	u64 vmx_msr;
+
+	rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
+	return vmx_msr & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
+}
+
 static inline bool cpu_has_vmx_posted_intr(void)
 {
 	return IS_ENABLED(CONFIG_X86_LOCAL_APIC) &&
@@ -3306,7 +3323,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
 		return -EIO;
 
 	min = PIN_BASED_EXT_INTR_MASK | PIN_BASED_NMI_EXITING;
-	opt = PIN_BASED_VIRTUAL_NMIS | PIN_BASED_POSTED_INTR;
+	opt = PIN_BASED_VIRTUAL_NMIS | PIN_BASED_POSTED_INTR |
+		 PIN_BASED_VMX_PREEMPTION_TIMER;
 	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_PINBASED_CTLS,
 				&_pin_based_exec_control) < 0)
 		return -EIO;
@@ -4779,6 +4797,8 @@ static u32 vmx_pin_based_exec_ctrl(struct vcpu_vmx *vmx)
 
 	if (!kvm_vcpu_apicv_active(&vmx->vcpu))
 		pin_based_exec_ctrl &= ~PIN_BASED_POSTED_INTR;
+	/* Enable the preemption timer dynamically */
+	pin_based_exec_ctrl &= ~PIN_BASED_VMX_PREEMPTION_TIMER;
 	return pin_based_exec_ctrl;
 }
 
@@ -10650,6 +10670,25 @@ static int vmx_check_intercept(struct kvm_vcpu *vcpu,
 	return X86EMUL_CONTINUE;
 }
 
+static int vmx_hwemul_timer(struct kvm_vcpu *vcpu)
+{
+	return hwemul_timer && cpu_has_preemption_timer();
+}
+
+static void vmx_set_hwemul_timer(struct kvm_vcpu *vcpu, u64 target_tsc)
+{
+	vmcs_write32(VMX_PREEMPTION_TIMER_VALUE,
+			target_tsc >> cpu_preemption_timer_multi());
+	vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL,
+			PIN_BASED_VMX_PREEMPTION_TIMER);
+}
+
+static void vmx_clear_hwemul_timer(struct kvm_vcpu *vcpu)
+{
+	vmcs_clear_bits(PIN_BASED_VM_EXEC_CONTROL,
+			PIN_BASED_VMX_PREEMPTION_TIMER);
+}
+
 static void vmx_sched_in(struct kvm_vcpu *vcpu, int cpu)
 {
 	if (ple_gap)
@@ -11018,6 +11057,10 @@ static struct kvm_x86_ops vmx_x86_ops = {
 	.pmu_ops = &intel_pmu_ops,
 
 	.update_pi_irte = vmx_update_pi_irte,
+
+	.hw_emul_timer = vmx_hwemul_timer,
+	.set_hwemul_timer = vmx_set_hwemul_timer,
+	.clear_hwemul_timer = vmx_clear_hwemul_timer,
 };
 
 static int __init vmx_init(void)
-- 
1.8.3.1

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