locking/qspinlock/x86: Only emit the test-and-set fallback when building guest support
[muen/linux.git] / arch / x86 / include / asm / qspinlock.h
1 #ifndef _ASM_X86_QSPINLOCK_H
2 #define _ASM_X86_QSPINLOCK_H
3
4 #include <asm/cpufeature.h>
5 #include <asm-generic/qspinlock_types.h>
6 #include <asm/paravirt.h>
7
8 #define queued_spin_unlock queued_spin_unlock
9 /**
10  * queued_spin_unlock - release a queued spinlock
11  * @lock : Pointer to queued spinlock structure
12  *
13  * A smp_store_release() on the least-significant byte.
14  */
15 static inline void native_queued_spin_unlock(struct qspinlock *lock)
16 {
17         smp_store_release((u8 *)lock, 0);
18 }
19
20 #ifdef CONFIG_PARAVIRT_SPINLOCKS
21 extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
22 extern void __pv_init_lock_hash(void);
23 extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
24 extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock);
25
26 static inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
27 {
28         pv_queued_spin_lock_slowpath(lock, val);
29 }
30
31 static inline void queued_spin_unlock(struct qspinlock *lock)
32 {
33         pv_queued_spin_unlock(lock);
34 }
35 #else
36 static inline void queued_spin_unlock(struct qspinlock *lock)
37 {
38         native_queued_spin_unlock(lock);
39 }
40 #endif
41
42 #ifdef CONFIG_PARAVIRT
43 #define virt_spin_lock virt_spin_lock
44 static inline bool virt_spin_lock(struct qspinlock *lock)
45 {
46         if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
47                 return false;
48
49         /*
50          * On hypervisors without PARAVIRT_SPINLOCKS support we fall
51          * back to a Test-and-Set spinlock, because fair locks have
52          * horrible lock 'holder' preemption issues.
53          */
54
55         do {
56                 while (atomic_read(&lock->val) != 0)
57                         cpu_relax();
58         } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
59
60         return true;
61 }
62 #endif /* CONFIG_PARAVIRT */
63
64 #include <asm-generic/qspinlock.h>
65
66 #endif /* _ASM_X86_QSPINLOCK_H */