[PATCH v7 07/11] pvqspinlock, x86: Allow unfair queue spinlock in a XEN guest

[Waiman Long <Waiman.Long@hp.com>]

This patch adds a XEN init function to activate the unfair queue
spinlock in a XEN guest when the PARAVIRT_UNFAIR_LOCKS kernel config
option is selected.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
---
 arch/x86/xen/setup.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 0982233..66bb6f5 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -625,3 +625,22 @@ void __init xen_arch_setup(void)
 	numa_off = 1;
 #endif
 }
+
+#ifdef CONFIG_PARAVIRT_UNFAIR_LOCKS
+/*
+ * Enable unfair lock if running in a Xen guest
+ */
+static __init int xen_unfair_locks_init_jump(void)
+{
+	/*
+	 * Disable unfair lock if not running in a PV domain
+	 */
+	if (!xen_pv_domain())
+		return 0;
+
+	static_key_slow_inc(&paravirt_unfairlocks_enabled);
+
+	return 0;
+}
+early_initcall(xen_unfair_locks_init_jump);
+#endif
-- 
1.7.1