x86: remove byte locks

Impact: cleanup

Remove byte locks implementation, which was introduced by Jeremy in
8efcbab6 ("paravirt: introduce a "lock-byte" spinlock implementation"),
but turned out to be dead code that is not used by any in-kernel
virtualization guest (Xen uses its own variant of spinlocks implementation
and KVM is not planning to move to byte locks).

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/paravirt.h

@@ -1389,8 +1389,6 @@ 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);
-
 #ifdef CONFIG_SMP
 
 static inline int __raw_spin_is_locked(struct raw_spinlock *lock)

arch/x86/include/asm/spinlock.h

@@ -172,70 +172,8 @@ static inline int __ticket_spin_is_contended(raw_spinlock_t *lock)
 	return (((tmp >> TICKET_SHIFT) - tmp) & ((1 << TICKET_SHIFT) - 1)) > 1;
 }
 
-#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");
+#ifndef CONFIG_PARAVIRT
 
-	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);
@@ -267,7 +205,7 @@ static __always_inline void __raw_spin_lock_flags(raw_spinlock_t *lock,
 	__raw_spin_lock(lock);
 }
 
-#endif	/* CONFIG_PARAVIRT */
+#endif
 
 static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)
 {

arch/x86/kernel/paravirt-spinlocks.c

@@ -26,13 +26,3 @@ struct pv_lock_ops pv_lock_ops = {
 };
 EXPORT_SYMBOL(pv_lock_ops);
 
-void __init paravirt_use_bytelocks(void)
-{
-#ifdef CONFIG_SMP
-	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;
-#endif
-}