[RFC PATCH 6/8] kvm: x86: enable/disable global/per-guest vcpu boost feature

[Vineeth Pillai (Google)]

Implement the module parameter for enable/disable of the feature
globally. Also implement the ioctls for enable/disable of the feature
per guest.

TODO: Documentation for the ioctls and kvm module parameters.

Co-developed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Vineeth Pillai (Google) <vineeth@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/x86.c       |  8 +++--
 include/linux/kvm_host.h | 34 +++++++++++++++++-
 include/uapi/linux/kvm.h |  5 +++
 virt/kvm/kvm_main.c      | 76 +++++++++++++++++++++++++++++++++++++---
 4 files changed, 116 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8c15c6ff352e..4fb73833fc68 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9949,8 +9949,12 @@ static void record_vcpu_boost_status(struct kvm_vcpu *vcpu)
 
 void kvm_set_vcpu_boosted(struct kvm_vcpu *vcpu, bool boosted)
 {
-	kvm_arch_vcpu_set_boost_status(&vcpu->arch,
-			boosted ? VCPU_BOOST_BOOSTED : VCPU_BOOST_NORMAL);
+	enum kvm_vcpu_boost_state boost_status = VCPU_BOOST_DISABLED;
+
+	if (kvm_pv_sched_enabled(vcpu->kvm))
+		boost_status = boosted ? VCPU_BOOST_BOOSTED : VCPU_BOOST_NORMAL;
+
+	kvm_arch_vcpu_set_boost_status(&vcpu->arch, boost_status);
 
 	kvm_make_request(KVM_REQ_VCPU_BOOST_UPDATE, vcpu);
 }
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f76680fbc60d..07f60a27025c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -807,6 +807,9 @@ struct kvm {
 	struct notifier_block pm_notifier;
 #endif
 	char stats_id[KVM_STATS_NAME_SIZE];
+#ifdef CONFIG_PARAVIRT_SCHED_KVM
+	bool pv_sched_enabled;
+#endif
 };
 
 #define kvm_err(fmt, ...) \
@@ -2292,9 +2295,38 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
 void kvm_set_vcpu_boosted(struct kvm_vcpu *vcpu, bool boosted);
 int kvm_vcpu_set_sched(struct kvm_vcpu *vcpu, bool boost);
 
+DECLARE_STATIC_KEY_FALSE(kvm_pv_sched);
+
+static inline bool kvm_pv_sched_enabled(struct kvm *kvm)
+{
+	if (static_branch_unlikely(&kvm_pv_sched))
+		return kvm->pv_sched_enabled;
+
+	return false;
+}
+
+static inline void kvm_set_pv_sched_enabled(struct kvm *kvm, bool enabled)
+{
+	unsigned long i;
+	struct kvm_vcpu *vcpu;
+
+	kvm->pv_sched_enabled = enabled;
+	/*
+	 * After setting vcpu_sched_enabled, we need to update each vcpu's
+	 * state(VCPU_BOOST_{DISABLED,NORMAL}) so that guest knows about the
+	 * update.
+	 * When disabling, we would also need to unboost vcpu threads
+	 * if already boosted.
+	 * XXX: this can race, needs locking!
+	 */
+	kvm_for_each_vcpu(i, vcpu, kvm)
+		kvm_vcpu_set_sched(vcpu, false);
+}
+
 static inline bool kvm_vcpu_sched_enabled(struct kvm_vcpu *vcpu)
 {
-	return kvm_arch_vcpu_pv_sched_enabled(&vcpu->arch);
+	return kvm_pv_sched_enabled(vcpu->kvm) &&
+		kvm_arch_vcpu_pv_sched_enabled(&vcpu->arch);
 }
 
 static inline void kvm_vcpu_kick_boost(struct kvm_vcpu *vcpu)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index f089ab290978..4beaeaa3e78f 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1192,6 +1192,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_COUNTER_OFFSET 227
 #define KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE 228
 #define KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES 229
+#define KVM_CAP_PV_SCHED	600
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -2249,4 +2250,8 @@ struct kvm_s390_zpci_op {
 /* flags for kvm_s390_zpci_op->u.reg_aen.flags */
 #define KVM_S390_ZPCIOP_REGAEN_HOST    (1 << 0)
 
+/* Available with KVM_CAP_PV_SCHED */
+#define KVM_SET_PV_SCHED_ENABLED	_IOW(KVMIO, 0xe0, int)
+#define KVM_GET_PV_SCHED_ENABLED	_IOR(KVMIO, 0xe1, int)
+
 #endif /* __LINUX_KVM_H */
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 0dd8b84ed073..d17cd28d5a92 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -99,6 +99,52 @@ unsigned int halt_poll_ns_shrink;
 module_param(halt_poll_ns_shrink, uint, 0644);
 EXPORT_SYMBOL_GPL(halt_poll_ns_shrink);
 
+#ifdef CONFIG_PARAVIRT_SCHED_KVM
+__read_mostly DEFINE_STATIC_KEY_FALSE(kvm_pv_sched);
+EXPORT_SYMBOL_GPL(kvm_pv_sched);
+
+static int set_kvm_pv_sched(const char *val, const struct kernel_param *cp)
+{
+	struct kvm *kvm;
+	char *s = strstrip((char *)val);
+	bool new_val, old_val = static_key_enabled(&kvm_pv_sched);
+
+	if (!strcmp(s, "0"))
+		new_val = 0;
+	else if (!strcmp(s, "1"))
+		new_val = 1;
+	else
+		return -EINVAL;
+
+	if (old_val != new_val) {
+		if (new_val)
+			static_branch_enable(&kvm_pv_sched);
+		else
+			static_branch_disable(&kvm_pv_sched);
+
+		mutex_lock(&kvm_lock);
+		list_for_each_entry(kvm, &vm_list, vm_list)
+			kvm_set_pv_sched_enabled(kvm, !old_val);
+		mutex_unlock(&kvm_lock);
+	}
+
+	return 0;
+}
+
+static int get_kvm_pv_sched(char *buf, const struct kernel_param *cp)
+{
+	return sprintf(buf, "%s\n",
+			static_key_enabled(&kvm_pv_sched) ? "1" : "0");
+}
+
+static const struct kernel_param_ops kvm_pv_sched_ops = {
+	.set = set_kvm_pv_sched,
+	.get = get_kvm_pv_sched
+};
+
+module_param_cb(kvm_pv_sched, &kvm_pv_sched_ops, NULL, 0644);
+#endif
+
 /*
  * Ordering of locks:
  *
@@ -1157,6 +1203,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 
 	BUILD_BUG_ON(KVM_MEM_SLOTS_NUM > SHRT_MAX);
 
+#ifdef CONFIG_PARAVIRT_SCHED_KVM
+	kvm->pv_sched_enabled = true;
+#endif
 	/*
 	 * Force subsequent debugfs file creations to fail if the VM directory
 	 * is not created (by kvm_create_vm_debugfs()).
@@ -3635,11 +3684,15 @@ int kvm_vcpu_set_sched(struct kvm_vcpu *vcpu, bool boost)
 	struct task_struct *vcpu_task = NULL;
 
 	/*
-	 * We can ignore the request if a boost request comes
-	 * when we are already boosted or an unboost request
-	 * when we are already unboosted.
+	 * If the feature is disabled and we receive a boost request,
+	 * we can ignore the request and set VCPU_BOOST_DISABLED for the
+	 * guest to see(kvm_set_vcpu_boosted).
+	 * Similarly, we can ignore the request if a boost request comes
+	 * when we are already boosted or an unboost request when we are
+	 * already unboosted.
 	 */
-	if (__can_ignore_set_sched(vcpu, boost))
+	if ((!kvm_vcpu_sched_enabled(vcpu) && boost) ||
+			__can_ignore_set_sched(vcpu, boost))
 		goto set_boost_status;
 
 	if (boost) {
@@ -4591,6 +4644,9 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 	case KVM_CAP_CHECK_EXTENSION_VM:
 	case KVM_CAP_ENABLE_CAP_VM:
 	case KVM_CAP_HALT_POLL:
+#ifdef CONFIG_PARAVIRT_SCHED_KVM
+	case KVM_CAP_PV_SCHED:
+#endif
 		return 1;
 #ifdef CONFIG_KVM_MMIO
 	case KVM_CAP_COALESCED_MMIO:
@@ -5018,6 +5074,18 @@ static long kvm_vm_ioctl(struct file *filp,
 	case KVM_GET_STATS_FD:
 		r = kvm_vm_ioctl_get_stats_fd(kvm);
 		break;
+#ifdef CONFIG_PARAVIRT_SCHED_KVM
+	case KVM_SET_PV_SCHED_ENABLED:
+		r = -EINVAL;
+		if (arg == 0 || arg == 1) {
+			kvm_set_pv_sched_enabled(kvm, arg);
+			r = 0;
+		}
+		break;
+	case KVM_GET_PV_SCHED_ENABLED:
+		r = kvm->pv_sched_enabled;
+		break;
+#endif
 	default:
 		r = kvm_arch_vm_ioctl(filp, ioctl, arg);
 	}
-- 
2.43.0