--- /dev/null
+#ifndef _ASM_X86_SPINLOCK_H
+#define _ASM_X86_SPINLOCK_H
+
+#include <linux/jump_label.h>
+#include <linux/atomic.h>
+#include <asm/page.h>
+#include <asm/processor.h>
+#include <linux/compiler.h>
+#include <asm/paravirt.h>
+#include <asm/bitops.h>
+
+/*
+ * Your basic SMP spinlocks, allowing only a single CPU anywhere
+ *
+ * Simple spin lock operations. There are two variants, one clears IRQ's
+ * on the local processor, one does not.
+ *
+ * These are fair FIFO ticket locks, which support up to 2^16 CPUs.
+ *
+ * (the type definitions are in asm/spinlock_types.h)
+ */
+
+#ifdef CONFIG_X86_32
+# define LOCK_PTR_REG "a"
+#else
+# define LOCK_PTR_REG "D"
+#endif
+
+#if defined(CONFIG_X86_32) && (defined(CONFIG_X86_PPRO_FENCE))
+/*
+ * On PPro SMP, we use a locked operation to unlock
+ * (PPro errata 66, 92)
+ */
+# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
+#else
+# define UNLOCK_LOCK_PREFIX
+#endif
+
+/* How long a lock should spin before we consider blocking */
+#define SPIN_THRESHOLD (1 << 15)
+
+extern struct static_key paravirt_ticketlocks_enabled;
+static __always_inline bool static_key_false(struct static_key *key);
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+
+static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
+{
+ set_bit(0, (volatile unsigned long *)&lock->tickets.head);
+}
+
+#else /* !CONFIG_PARAVIRT_SPINLOCKS */
+static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
+ __ticket_t ticket)
+{
+}
+static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
+ __ticket_t ticket)
+{
+}
+
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
+static inline int __tickets_equal(__ticket_t one, __ticket_t two)
+{
+ return !((one ^ two) & ~TICKET_SLOWPATH_FLAG);
+}
+
+static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
+ __ticket_t head)
+{
+ if (head & TICKET_SLOWPATH_FLAG) {
+ arch_spinlock_t old, new;
+
+ old.tickets.head = head;
+ new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
+ old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
+ new.tickets.tail = old.tickets.tail;
+
+ /* try to clear slowpath flag when there are no contenders */
+ cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
+ }
+}
+
+static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+{
+ return __tickets_equal(lock.tickets.head, lock.tickets.tail);
+}
+
+/*
+ * Ticket locks are conceptually two parts, one indicating the current head of
+ * the queue, and the other indicating the current tail. The lock is acquired
+ * by atomically noting the tail and incrementing it by one (thus adding
+ * ourself to the queue and noting our position), then waiting until the head
+ * becomes equal to the the initial value of the tail.
+ *
+ * We use an xadd covering *both* parts of the lock, to increment the tail and
+ * also load the position of the head, which takes care of memory ordering
+ * issues and should be optimal for the uncontended case. Note the tail must be
+ * in the high part, because a wide xadd increment of the low part would carry
+ * up and contaminate the high part.
+ */
+static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
+{
+ register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
+
+ inc = xadd(&lock->tickets, inc);
+ if (likely(inc.head == inc.tail))
+ goto out;
+
+ for (;;) {
+ unsigned count = SPIN_THRESHOLD;
+
+ do {
+ inc.head = READ_ONCE(lock->tickets.head);
+ if (__tickets_equal(inc.head, inc.tail))
+ goto clear_slowpath;
+ cpu_relax();
+ } while (--count);
+ __ticket_lock_spinning(lock, inc.tail);
+ }
+clear_slowpath:
+ __ticket_check_and_clear_slowpath(lock, inc.head);
+out:
+ barrier(); /* make sure nothing creeps before the lock is taken */
+}
+
+static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
+{
+ arch_spinlock_t old, new;
+
+ old.tickets = READ_ONCE(lock->tickets);
+ if (!__tickets_equal(old.tickets.head, old.tickets.tail))
+ return 0;
+
+ new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
+ new.head_tail &= ~TICKET_SLOWPATH_FLAG;
+
+ /* cmpxchg is a full barrier, so nothing can move before it */
+ return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
+}
+
+static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
+{
+ if (TICKET_SLOWPATH_FLAG &&
+ static_key_false(¶virt_ticketlocks_enabled)) {
+ __ticket_t head;
+
+ BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
+
+ head = xadd(&lock->tickets.head, TICKET_LOCK_INC);
+
+ if (unlikely(head & TICKET_SLOWPATH_FLAG)) {
+ head &= ~TICKET_SLOWPATH_FLAG;
+ __ticket_unlock_kick(lock, (head + TICKET_LOCK_INC));
+ }
+ } else
+ __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
+}
+
+static inline int arch_spin_is_locked(arch_spinlock_t *lock)
+{
+ struct __raw_tickets tmp = READ_ONCE(lock->tickets);
+
+ return !__tickets_equal(tmp.tail, tmp.head);
+}
+
+static inline int arch_spin_is_contended(arch_spinlock_t *lock)
+{
+ struct __raw_tickets tmp = READ_ONCE(lock->tickets);
+
+ tmp.head &= ~TICKET_SLOWPATH_FLAG;
+ return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
+}
+#define arch_spin_is_contended arch_spin_is_contended
+
+static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
+ unsigned long flags)
+{
+ arch_spin_lock(lock);
+}
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ __ticket_t head = READ_ONCE(lock->tickets.head);
+
+ for (;;) {
+ struct __raw_tickets tmp = READ_ONCE(lock->tickets);
+ /*
+ * We need to check "unlocked" in a loop, tmp.head == head
+ * can be false positive because of overflow.
+ */
+ if (__tickets_equal(tmp.head, tmp.tail) ||
+ !__tickets_equal(tmp.head, head))
+ break;
+
+ cpu_relax();
+ }
+}
+
+/*
+ * Read-write spinlocks, allowing multiple readers
+ * but only one writer.
+ *
+ * NOTE! it is quite common to have readers in interrupts
+ * but no interrupt writers. For those circumstances we
+ * can "mix" irq-safe locks - any writer needs to get a
+ * irq-safe write-lock, but readers can get non-irqsafe
+ * read-locks.
+ *
+ * On x86, we implement read-write locks using the generic qrwlock with
+ * x86 specific optimization.
+ */
+
+#include <asm/qrwlock.h>
+
+#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
+#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
+
+#define arch_spin_relax(lock) cpu_relax()
+#define arch_read_relax(lock) cpu_relax()
+#define arch_write_relax(lock) cpu_relax()
+
+#endif /* _ASM_X86_SPINLOCK_H */
Code Review / kvmfornfv.git / blobdiff