locking/paravirt: Use new static key for controlling call of virt_spin_lock()

There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
has the downside of falling back to unfair test and set scheme for
qspinlocks due to virt_spin_lock() detecting the virtualized
environment.

Add a static key controlling whether virt_spin_lock() should be
called or not. When running on bare metal set the new key to false.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akataria@vmware.com
Cc: boris.ostrovsky@oracle.com
Cc: chrisw@sous-sol.org
Cc: hpa@zytor.com
Cc: jeremy@goop.org
Cc: rusty@rustcorp.com.au
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/20170906173625.18158-2-jgross@suse.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 24 insertions, 3 deletions

diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 48a706f641f2..308dfd0714c7 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -1,6 +1,7 @@
 #ifndef _ASM_X86_QSPINLOCK_H
 #define _ASM_X86_QSPINLOCK_H
 
+#include <linux/jump_label.h>
 #include <asm/cpufeature.h>
 #include <asm-generic/qspinlock_types.h>
 #include <asm/paravirt.h>
@@ -46,10 +47,14 @@ static inline void queued_spin_unlock(struct qspinlock *lock)
 #endif
 
 #ifdef CONFIG_PARAVIRT
+DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);
+
+void native_pv_lock_init(void) __init;
+
 #define virt_spin_lock virt_spin_lock
 static inline bool virt_spin_lock(struct qspinlock *lock)
 {
-	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+	if (!static_branch_likely(&virt_spin_lock_key))
 		return false;
 
 	/*
@@ -65,6 +70,10 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
 
 	return true;
 }
+#else
+static inline void native_pv_lock_init(void)
+{
+}
 #endif /* CONFIG_PARAVIRT */
 
 #include <asm-generic/qspinlock.h>
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 19a3e8f961c7..041096bdef86 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -115,8 +115,18 @@ unsigned paravirt_patch_jmp(void *insnbuf, const void *target,
 	return 5;
 }
 
-/* Neat trick to map patch type back to the call within the
- * corresponding structure. */
+DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
+
+void __init native_pv_lock_init(void)
+{
+	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+		static_branch_disable(&virt_spin_lock_key);
+}
+
+/*
+ * Neat trick to map patch type back to the call within the
+ * corresponding structure.
+ */
 static void *get_call_destination(u8 type)
 {
 	struct paravirt_patch_template tmpl = {
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ad59edd84de7..361f91674ce5 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -77,6 +77,7 @@
 #include <asm/i8259.h>
 #include <asm/realmode.h>
 #include <asm/misc.h>
+#include <asm/qspinlock.h>
 
 /* Number of siblings per CPU package */
 int smp_num_siblings = 1;
@@ -1384,6 +1385,7 @@ void __init native_smp_prepare_boot_cpu(void)
 	/* already set me in cpu_online_mask in boot_cpu_init() */
 	cpumask_set_cpu(me, cpu_callout_mask);
 	cpu_set_state_online(me);
+	native_pv_lock_init();
 }
 
 void __init native_smp_cpus_done(unsigned int max_cpus)