Pull up following revision(s) (requested by riastradh in ticket #1170):

	sys/arch/xen/xen/xen_clock.c: revision 1.22

xen: Use ordered rdtsc() function, rather than inline rdtsc asm.

This will issue either lfence, mfence, or cpuid before the rdtsc
instruction, depending on the CPU identification, in order to prevent
reordering with respect to surrounding loads -- particularly those
used to query the host's systime parameters.

May help with:
PR port-xen/59437: Xen time stability

Author: MartinHusemann

sys/arch/xen/xen/xen_clock.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: xen_clock.c,v 1.8.18.2 2024/10/13 14:38:13 martin Exp $	*/
+/*	$NetBSD: xen_clock.c,v 1.8.18.3 2025/10/03 09:58:44 martin Exp $	*/
 
 /*-
  * Copyright (c) 2017, 2018 The NetBSD Foundation, Inc.
@@ -36,7 +36,7 @@
 #endif
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: xen_clock.c,v 1.8.18.2 2024/10/13 14:38:13 martin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xen_clock.c,v 1.8.18.3 2025/10/03 09:58:44 martin Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -114,26 +114,12 @@ static void	xen_timepush_intr(void *);
 static int	sysctl_xen_timepush(SYSCTLFN_ARGS);
 #endif
 
-/*
- * xen_rdtsc()
- *
- *	Read the local pCPU's tsc.
- */
-static inline uint64_t
-xen_rdtsc(void)
-{
-	uint32_t lo, hi;
-
-	asm volatile("rdtsc" : "=a"(lo), "=d"(hi));
-
-	return ((uint64_t)hi << 32) | lo;
-}
-
 /*
  * struct xen_vcputime_ticket
  *
  *	State for a vCPU read section, during which a caller may read
- *	from fields of a struct vcpu_time_info and call xen_rdtsc.
+ *	from fields of a struct vcpu_time_info and call rdtsc.
+ *
  *	Caller must enter with xen_vcputime_enter, exit with
  *	xen_vcputime_exit, and be prepared to retry if
  *	xen_vcputime_exit fails.
@@ -256,7 +242,7 @@ xen_vcputime_systime_ns(void)
 		tsc_shift = vt->tsc_shift;
 
 		/* Read the CPU's tsc.  */
-		tsc = xen_rdtsc();
+		tsc = rdtsc();
 	} while (!xen_vcputime_exit(vt, &ticket));
 
 	/*
@@ -538,7 +524,7 @@ xen_delay(unsigned n)
 		/* Get the starting tsc and tsc frequency.  */
 		do {
 			vt = xen_vcputime_enter(&ticket);
-			tsc_start = last_tsc = xen_rdtsc();
+			tsc_start = last_tsc = rdtsc();
 			tsc_to_system_mul = vt->tsc_to_system_mul;
 			tsc_shift = vt->tsc_shift;
 		} while (!xen_vcputime_exit(vt, &ticket));
@@ -549,7 +535,7 @@ xen_delay(unsigned n)
 		 * backwards meaning we've probably migrated pCPUs.
 		 */
 		for (;;) {
-			tsc = xen_rdtsc();
+			tsc = rdtsc();
 			if (__predict_false(tsc < last_tsc))
 				break;
 			if (xen_tsc_to_ns_delta(tsc - tsc_start,