Re: [PATCH RFC v5 8/8] pvqspinlock, x86: Enable KVM to use qspinlock's PV support

This patch enables KVM to use the queue spinlock's PV support code
when the PARAVIRT_SPINLOCKS kernel config option is set. However,
PV support for Xen is not ready yet and so the queue spinlock will
still have to be disabled when PARAVIRT_SPINLOCKS config option is
on with Xen.

Signed-off-by: Waiman Long <redacted>
---
 arch/x86/kernel/kvm.c |   54 +++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/Kconfig.locks  |    2 +-
 2 files changed, 55 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index f318e78..3ddc436 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c

@@ -568,6 +568,7 @@ static void kvm_kick_cpu(int cpu)
 	kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
 }
 
+#ifndef CONFIG_QUEUE_SPINLOCK
 enum kvm_contention_stat {
 	TAKEN_SLOW,
 	TAKEN_SLOW_PICKUP,

@@ -795,6 +796,55 @@ static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
 		}
 	}
 }
+#else /* !CONFIG_QUEUE_SPINLOCK */
+
+#ifdef CONFIG_KVM_DEBUG_FS
+static struct dentry *d_spin_debug;
+static struct dentry *d_kvm_debug;
+static u32 lh_kick_stats;	/* Lock holder kick count */
+static u32 qh_kick_stats;	/* Queue head kick count  */
+static u32 nn_kick_stats;	/* Next node kick count   */
+
+static int __init kvm_spinlock_debugfs(void)
+{
+	d_kvm_debug = debugfs_create_dir("kvm-guest", NULL);
+	if (!d_kvm_debug) {
+		printk(KERN_WARNING
+		       "Could not create 'kvm' debugfs directory\n");
+		return -ENOMEM;
+	}
+	d_spin_debug = debugfs_create_dir("spinlocks", d_kvm_debug);
+
+	debugfs_create_u32("lh_kick_stats", 0644, d_spin_debug, &lh_kick_stats);
+	debugfs_create_u32("qh_kick_stats", 0644, d_spin_debug, &qh_kick_stats);
+	debugfs_create_u32("nn_kick_stats", 0644, d_spin_debug, &nn_kick_stats);
+
+	return 0;
+}
+
+static inline void inc_kick_stats(enum pv_kick_type type)
+{
+	if (type == PV_KICK_LOCK_HOLDER)
+		add_smp(&lh_kick_stats, 1);
+	else if (type == PV_KICK_QUEUE_HEAD)
+		add_smp(&qh_kick_stats, 1);
+	else
+		add_smp(&nn_kick_stats, 1);
+}
+fs_initcall(kvm_spinlock_debugfs);
+
+#else /* CONFIG_KVM_DEBUG_FS */
+static inline void inc_kick_stats(enum pv_kick_type type)
+{
+}
+#endif /* CONFIG_KVM_DEBUG_FS */
+
+static void kvm_kick_cpu_type(int cpu, enum pv_kick_type type)
+{
+	kvm_kick_cpu(cpu);
+	inc_kick_stats(type);
+}
+#endif /* !CONFIG_QUEUE_SPINLOCK */
 
 /*
  * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.

@@ -807,8 +857,12 @@ void __init kvm_spinlock_init(void)
 	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
 		return;
 
+#ifdef CONFIG_QUEUE_SPINLOCK
+	pv_lock_ops.kick_cpu = kvm_kick_cpu_type;
+#else
 	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
 	pv_lock_ops.unlock_kick = kvm_unlock_kick;
+#endif
 }
 
 static __init int kvm_spinlock_init_jump(void)

diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
index f185584..a70fdeb 100644
--- a/kernel/Kconfig.locks
+++ b/kernel/Kconfig.locks

@@ -229,4 +229,4 @@ config ARCH_USE_QUEUE_SPINLOCK
 
 config QUEUE_SPINLOCK
 	def_bool y if ARCH_USE_QUEUE_SPINLOCK
-	depends on SMP && !PARAVIRT_SPINLOCKS
+	depends on SMP && (!PARAVIRT_SPINLOCKS || !XEN)