3 files changed, 75 insertions, 1 deletions

diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index f33816868707..bba4041bb7ff 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -268,6 +268,15 @@ enum paravirt_lazy_mode paravirt_get_lazy_mode(void)
         return __get_cpu_var(paravirt_lazy_mode);
 }
 
+void __init paravirt_use_bytelocks(void)
+{
+        pv_lock_ops.spin_is_locked = __byte_spin_is_locked;
+        pv_lock_ops.spin_is_contended = __byte_spin_is_contended;
+        pv_lock_ops.spin_lock = __byte_spin_lock;
+        pv_lock_ops.spin_trylock = __byte_spin_trylock;
+        pv_lock_ops.spin_unlock = __byte_spin_unlock;
+}
+
 struct pv_info pv_info = {
         .name = "bare hardware",
         .paravirt_enabled = 0,
diff --git a/include/asm-x86/paravirt.h b/include/asm-x86/paravirt.h
index feb6bb66c5e2..65ed02cdbbd7 100644
--- a/include/asm-x86/paravirt.h
+++ b/include/asm-x86/paravirt.h
@@ -1385,6 +1385,8 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx,
 void _paravirt_nop(void);
 #define paravirt_nop    ((void *)_paravirt_nop)
 
+void paravirt_use_bytelocks(void);
+
 static inline int __raw_spin_is_locked(struct raw_spinlock *lock)
 {
         return PVOP_CALL1(int, pv_lock_ops.spin_is_locked, lock);
diff --git a/include/asm-x86/spinlock.h b/include/asm-x86/spinlock.h
index 9726144cdaba..4f9a9861799a 100644
--- a/include/asm-x86/spinlock.h
+++ b/include/asm-x86/spinlock.h
@@ -184,7 +184,70 @@ static __always_inline void __ticket_spin_unlock(raw_spinlock_t *lock)
 
 #define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
 
-#ifndef CONFIG_PARAVIRT
+#ifdef CONFIG_PARAVIRT
+/*
+ * Define virtualization-friendly old-style lock byte lock, for use in
+ * pv_lock_ops if desired.
+ *
+ * This differs from the pre-2.6.24 spinlock by always using xchgb
+ * rather than decb to take the lock; this allows it to use a
+ * zero-initialized lock structure.  It also maintains a 1-byte
+ * contention counter, so that we can implement
+ * __byte_spin_is_contended.
+ */
+struct __byte_spinlock {
+        s8 lock;
+        s8 spinners;
+};
+
+static inline int __byte_spin_is_locked(raw_spinlock_t *lock)
+{
+        struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;
+        return bl->lock != 0;
+}
+
+static inline int __byte_spin_is_contended(raw_spinlock_t *lock)
+{
+        struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;
+        return bl->spinners != 0;
+}
+
+static inline void __byte_spin_lock(raw_spinlock_t *lock)
+{
+        struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;
+        s8 val = 1;
+
+        asm("1: xchgb %1, %0\n"
+            "   test %1,%1\n"
+            "   jz 3f\n"
+            "   " LOCK_PREFIX "incb %2\n"
+            "2: rep;nop\n"
+            "   cmpb $1, %0\n"
+            "   je 2b\n"
+            "   " LOCK_PREFIX "decb %2\n"
+            "   jmp 1b\n"
+            "3:"
+            : "+m" (bl->lock), "+q" (val), "+m" (bl->spinners): : "memory");
+}
+
+static inline int __byte_spin_trylock(raw_spinlock_t *lock)
+{
+        struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;
+        u8 old = 1;
+
+        asm("xchgb %1,%0"
+            : "+m" (bl->lock), "+q" (old) : : "memory");
+
+        return old == 0;
+}
+
+static inline void __byte_spin_unlock(raw_spinlock_t *lock)
+{
+        struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;
+        smp_wmb();
+        bl->lock = 0;
+}
+#else  /* !CONFIG_PARAVIRT */
 static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
 {
         return __ticket_spin_is_locked(lock);