 @@ -1,14 +1,14 @@
-/*	$NetBSD: idt.c,v 1.15 2021/12/23 02:07:21 yamaguchi Exp $	*/
+/*	$NetBSD: idt.c,v 1.16 2022/02/13 19:21:21 riastradh Exp $	*/
 /*-
  * Copyright (c) 1996, 1997, 1998, 2000, 2009 The NetBSD Foundation, Inc.
  * All rights reserved.
+ *
  * This code is derived from software contributed to The NetBSD Foundation
  * by Charles M. Hannum, by Jason R. Thorpe of the Numerical Aerospace
  * Simulation Facility NASA Ames Research Center, and by Andrew Doran.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
 @@ -55,27 +55,27 @@
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
+ *
  *	@(#)machdep.c	7.4 (Berkeley) 6/3/91
  */
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: idt.c,v 1.15 2021/12/23 02:07:21 yamaguchi Exp $");
+__KERNEL_RCSID(0, "$NetBSD: idt.c,v 1.16 2022/02/13 19:21:21 riastradh Exp $");
 #include "opt_pcpu_idt.h"
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/mutex.h>
 #include <sys/cpu.h>
 #include <sys/atomic.h>
 #include <uvm/uvm.h>
 #include <machine/segments.h>
 @@ -164,77 +164,82 @@ unset_idtgate(struct gate_descriptor *id
  */
 int
 idt_vec_alloc(struct idt_vec *iv, int low, int high)
+{
 	int vec;
 	char *idt_allocmap = iv->iv_allocmap;
 	KASSERT(mutex_owned(&cpu_lock) || !mp_online);
 	if (low < 0 || high >= __arraycount(iv->iv_allocmap))
 		return -1;
 	for (vec = low; vec <= high; vec++) {
-		if (idt_allocmap[vec] == 0) {
+		/* pairs with atomic_store_release in idt_vec_free */
-			/* idt_vec_free() can be unlocked, so membar. */
+		if (atomic_load_acquire(&idt_allocmap[vec]) == 0) {
-			membar_sync();
+			/*
-			idt_allocmap[vec] = 1;
+			 * No ordering needed here (`relaxed') because
 			 * access to free entries is serialized by
 			 * cpu_lock or single-threaded operation.
 			 */
 			atomic_store_relaxed(&idt_allocmap[vec], 1);
 			return vec;
+		}
+	}
 	return -1;
+}
 void
 idt_vec_reserve(struct idt_vec *iv, int vec)
+{
 	int result;
 	KASSERT(mutex_owned(&cpu_lock) || !mp_online);
 	result = idt_vec_alloc(iv, vec, vec);
 	if (result < 0) {
 		panic("%s: failed to reserve vec %d", __func__, vec);
+	}
+}
 void
 idt_vec_set(struct idt_vec *iv, int vec, void (*function)(void))
+{
 	idt_descriptor_t *idt;
 	char *idt_allocmap __diagused = iv->iv_allocmap;
-	KASSERT(idt_allocmap[vec] == 1);
+	KASSERT(atomic_load_relaxed(&idt_allocmap[vec]) == 1);
 	idt = iv->iv_idt;
 	set_idtgate(&idt[vec], function, 0, SDT_SYS386IGT, SEL_KPL,
 	       GSEL(GCODE_SEL, SEL_KPL));
+}
 /*
  * Free IDT vector.  No locking required as release is atomic.
  */
 void
 idt_vec_free(struct idt_vec *iv, int vec)
+{
 	idt_descriptor_t *idt;
 	char *idt_allocmap = iv->iv_allocmap;
-	KASSERT(idt_allocmap[vec] == 1);
+	KASSERT(atomic_load_relaxed(&idt_allocmap[vec]) == 1);
 	idt = iv->iv_idt;
 	unset_idtgate(&idt[vec]);
-	idt_allocmap[vec] = 0;
+	/* pairs with atomic_load_acquire in idt_vec_alloc */
 	atomic_store_release(&idt_allocmap[vec], 0);
+}
 bool
 idt_vec_is_pcpu(void)
+{
 #ifdef PCPU_IDT
 	return true;
 #else
 	return false;
 #endif
+}