1 files changed, 118 insertions, 0 deletions
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
new file mode 100644
index 000000000..a334dd0d7
--- /dev/null
+++ b/arch/x86/include/asm/preempt.h
@@ -0,0 +1,118 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_PREEMPT_H
+#define __ASM_PREEMPT_H
+
+#include <asm/rmwcc.h>
+#include <asm/percpu.h>
+#include <linux/thread_info.h>
+
+DECLARE_PER_CPU(int, __preempt_count);
+
+/* We use the MSB mostly because its available */
+#define PREEMPT_NEED_RESCHED	0x80000000
+
+/*
+ * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
+ * that a decrement hitting 0 means we can and should reschedule.
+ */
+#define PREEMPT_ENABLED	(0 + PREEMPT_NEED_RESCHED)
+
+/*
+ * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
+ * that think a non-zero value indicates we cannot preempt.
+ */
+static __always_inline int preempt_count(void)
+{
+	return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
+}
+
+static __always_inline void preempt_count_set(int pc)
+{
+	int old, new;
+
+	do {
+		old = raw_cpu_read_4(__preempt_count);
+		new = (old & PREEMPT_NEED_RESCHED) |
+			(pc & ~PREEMPT_NEED_RESCHED);
+	} while (raw_cpu_cmpxchg_4(__preempt_count, old, new) != old);
+}
+
+/*
+ * must be macros to avoid header recursion hell
+ */
+#define init_task_preempt_count(p) do { } while (0)
+
+#define init_idle_preempt_count(p, cpu) do { \
+	per_cpu(__preempt_count, (cpu)) = PREEMPT_DISABLED; \
+} while (0)
+
+/*
+ * We fold the NEED_RESCHED bit into the preempt count such that
+ * preempt_enable() can decrement and test for needing to reschedule with a
+ * single instruction.
+ *
+ * We invert the actual bit, so that when the decrement hits 0 we know we both
+ * need to resched (the bit is cleared) and can resched (no preempt count).
+ */
+
+static __always_inline void set_preempt_need_resched(void)
+{
+	raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
+}
+
+static __always_inline void clear_preempt_need_resched(void)
+{
+	raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
+}
+
+static __always_inline bool test_preempt_need_resched(void)
+{
+	return !(raw_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
+}
+
+/*
+ * The various preempt_count add/sub methods
+ */
+
+static __always_inline void __preempt_count_add(int val)
+{
+	raw_cpu_add_4(__preempt_count, val);
+}
+
+static __always_inline void __preempt_count_sub(int val)
+{
+	raw_cpu_add_4(__preempt_count, -val);
+}
+
+/*
+ * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
+ * a decrement which hits zero means we have no preempt_count and should
+ * reschedule.
+ */
+static __always_inline bool __preempt_count_dec_and_test(void)
+{
+	return GEN_UNARY_RMWcc("decl", __preempt_count, e, __percpu_arg([var]));
+}
+
+/*
+ * Returns true when we need to resched and can (barring IRQ state).
+ */
+static __always_inline bool should_resched(int preempt_offset)
+{
+	return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
+}
+
+#ifdef CONFIG_PREEMPTION
+  extern asmlinkage void preempt_schedule_thunk(void);
+# define __preempt_schedule() \
+	asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT)
+
+  extern asmlinkage void preempt_schedule(void);
+  extern asmlinkage void preempt_schedule_notrace_thunk(void);
+# define __preempt_schedule_notrace() \
+	asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT)
+
+  extern asmlinkage void preempt_schedule_notrace(void);
+#endif
+
+#endif /* __ASM_PREEMPT_H */