diff options
Diffstat (limited to 'arch/x86/include/asm/qspinlock.h')
| -rw-r--r-- | arch/x86/include/asm/qspinlock.h | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index cde8357bb2..68da67df30 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -66,13 +66,15 @@ static inline bool vcpu_is_preempted(long cpu) #ifdef CONFIG_PARAVIRT /* - * virt_spin_lock_key - enables (by default) the virt_spin_lock() hijack. + * virt_spin_lock_key - disables by default the virt_spin_lock() hijack. * - * Native (and PV wanting native due to vCPU pinning) should disable this key. - * It is done in this backwards fashion to only have a single direction change, - * which removes ordering between native_pv_spin_init() and HV setup. + * Native (and PV wanting native due to vCPU pinning) should keep this key + * disabled. Native does not touch the key. + * + * When in a guest then native_pv_lock_init() enables the key first and + * KVM/XEN might conditionally disable it later in the boot process again. */ -DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); +DECLARE_STATIC_KEY_FALSE(virt_spin_lock_key); /* * Shortcut for the queued_spin_lock_slowpath() function that allows @@ -85,6 +87,8 @@ DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); #define virt_spin_lock virt_spin_lock static inline bool virt_spin_lock(struct qspinlock *lock) { + int val; + if (!static_branch_likely(&virt_spin_lock_key)) return false; @@ -94,10 +98,13 @@ static inline bool virt_spin_lock(struct qspinlock *lock) * horrible lock 'holder' preemption issues. */ - do { - while (atomic_read(&lock->val) != 0) - cpu_relax(); - } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0); + __retry: + val = atomic_read(&lock->val); + + if (val || !atomic_try_cmpxchg(&lock->val, &val, _Q_LOCKED_VAL)) { + cpu_relax(); + goto __retry; + } return true; } |