Since we are here and at least I do hw.cpuspeed measurements, I like to
make it mp-safe. Introduce temporary `cpu_cpuspeed_mpsafe' handler
pointer and call it lockless if it is set. Kernel lock is pretty enough
to call old `cpu_cpuspeed' handler, so we avoid `sysctl_lock'
acquisition and useless pages wiring. The rest architectures can be
adjusted separately.

ok?

Index: sys/arch/amd64/amd64/identcpu.c
===================================================================
RCS file: /cvs/src/sys/arch/amd64/amd64/identcpu.c,v
retrieving revision 1.150
diff -u -p -r1.150 identcpu.c
--- sys/arch/amd64/amd64/identcpu.c	29 Apr 2025 20:19:48 -0000	1.150
+++ sys/arch/amd64/amd64/identcpu.c	20 May 2025 21:30:47 -0000
@@ -61,9 +61,14 @@ void	tsc_timecounter_init(struct cpu_inf
 void	cpu_check_vmm_cap(struct cpu_info *);
 #endif /* NVMM > 0 */
 
+/*
+ * Locks used to protect data:
+ *	a	atomic
+ */
+
 /* sysctl wants this. */
 char cpu_model[48];
-int cpuspeed;
+int cpuspeed;			/* [a] */
 
 int amd64_has_xcrypt;
 int amd64_pos_cbit;	/* C bit position for SEV */
@@ -74,7 +79,7 @@ int has_rdseed;
 int
 cpu_amd64speed(int *freq)
 {
-	*freq = cpuspeed;
+	*freq = atomic_load_int(&cpuspeed);
 	return (0);
 }
 
@@ -620,7 +625,7 @@ identifycpu(struct cpu_info *ci)
 
 	if (CPU_IS_PRIMARY(ci)) {
 		cpuspeed = (freq + 4999) / 1000000;
-		cpu_cpuspeed = cpu_amd64speed;
+		cpu_cpuspeed_mpsafe = cpu_amd64speed;
 	}
 
 	printf(", %02x-%02x-%02x", ci->ci_family, ci->ci_model,
Index: sys/arch/amd64/amd64/k1x-pstate.c
===================================================================
RCS file: /cvs/src/sys/arch/amd64/amd64/k1x-pstate.c,v
retrieving revision 1.11
diff -u -p -r1.11 k1x-pstate.c
--- sys/arch/amd64/amd64/k1x-pstate.c	11 Aug 2021 18:31:48 -0000	1.11
+++ sys/arch/amd64/amd64/k1x-pstate.c	20 May 2025 21:30:48 -0000
@@ -26,6 +26,7 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/atomic.h>
 #include <sys/malloc.h>
 #include <sys/sysctl.h>
 
@@ -106,7 +107,7 @@ k1x_transition(struct k1x_cpu_state *cst
 		DELAY(100);
 	}
 	if (cfid == fid) {
-		cpuspeed = cstate->state_table[level].freq;
+		atomic_store_int(&cpuspeed, cstate->state_table[level].freq);
 #if 0
 		(void)printf("Target: %d Current: %d Pstate: %d\n",
 		    cstate->state_table[level].freq,
Index: sys/arch/amd64/amd64/powernow-k8.c
===================================================================
RCS file: /cvs/src/sys/arch/amd64/amd64/powernow-k8.c,v
retrieving revision 1.29
diff -u -p -r1.29 powernow-k8.c
--- sys/arch/amd64/amd64/powernow-k8.c	21 Feb 2022 08:16:08 -0000	1.29
+++ sys/arch/amd64/amd64/powernow-k8.c	20 May 2025 21:30:48 -0000
@@ -28,6 +28,7 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/atomic.h>
 #include <sys/malloc.h>
 #include <sys/sysctl.h>
 
@@ -271,7 +272,7 @@ k8pnow_transition(struct k8pnow_cpu_stat
 	}
 
 	if (cfid == fid || cvid == vid)
-		cpuspeed = cstate->state_table[level].freq;
+		atomic_store_int(&cpuspeed, cstate->state_table[level].freq);
 }
 
 /*
Index: sys/kern/kern_sysctl.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_sysctl.c,v
retrieving revision 1.468
diff -u -p -r1.468 kern_sysctl.c
--- sys/kern/kern_sysctl.c	9 May 2025 14:53:22 -0000	1.468
+++ sys/kern/kern_sysctl.c	20 May 2025 21:30:49 -0000
@@ -171,6 +171,7 @@ int hw_sysctl_locked(int *, u_int, void 
 	struct proc *);
 
 int (*cpu_cpuspeed)(int *);
+int (*cpu_cpuspeed_mpsafe)(int *);
 
 /*
  * Lock to avoid too many processes vslocking a large amount of memory
@@ -844,9 +845,24 @@ hw_sysctl(int *name, u_int namelen, void
 	case HW_USERMEM:
 		return (sysctl_rdint(oldp, oldlenp, newp,
 		    ptoa(physmem - uvmexp.wired)));
+	case HW_CPUSPEED: {
+		int cpuspeed;
+
+		if (cpu_cpuspeed_mpsafe)
+			err = cpu_cpuspeed_mpsafe(&cpuspeed);
+		else if (cpu_cpuspeed) {
+			KERNEL_LOCK();
+			err = cpu_cpuspeed(&cpuspeed);
+			KERNEL_UNLOCK();
+		} else
+			err = EOPNOTSUPP;
+
+		if (err)
+			return (err);
+		return (sysctl_rdint(oldp, oldlenp, newp, cpuspeed));
+	}
 	case HW_DISKNAMES:
 	case HW_DISKSTATS:
-	case HW_CPUSPEED:
 #ifndef	SMALL_KERNEL
 	case HW_SENSORS:
 	case HW_SETPERF:
@@ -911,7 +927,7 @@ int
 hw_sysctl_locked(int *name, u_int namelen, void *oldp, size_t *oldlenp,
     void *newp, size_t newlen, struct proc *p)
 {
-	int err, cpuspeed;
+	int err;
 
 	switch (name[0]) {
 	case HW_DISKNAMES:
@@ -929,13 +945,6 @@ hw_sysctl_locked(int *name, u_int namele
 			return err;
 		return (sysctl_rdstruct(oldp, oldlenp, newp, diskstats,
 		    disk_count * sizeof(struct diskstats)));
-	case HW_CPUSPEED:
-		if (!cpu_cpuspeed)
-			return (EOPNOTSUPP);
-		err = cpu_cpuspeed(&cpuspeed);
-		if (err)
-			return err;
-		return (sysctl_rdint(oldp, oldlenp, newp, cpuspeed));
 #ifndef SMALL_KERNEL
 	case HW_SENSORS:
 		return (sysctl_sensors(name + 1, namelen - 1, oldp, oldlenp,
Index: sys/sys/sysctl.h
===================================================================
RCS file: /cvs/src/sys/sys/sysctl.h,v
retrieving revision 1.242
diff -u -p -r1.242 sysctl.h
--- sys/sys/sysctl.h	29 Apr 2025 02:24:32 -0000	1.242
+++ sys/sys/sysctl.h	20 May 2025 21:30:49 -0000
@@ -1084,6 +1084,7 @@ int sysctl_sysvipc(int *, u_int, void *,
 int sysctl_wdog(int *, u_int, void *, size_t *, void *, size_t);
 
 extern int (*cpu_cpuspeed)(int *);
+extern int (*cpu_cpuspeed_mpsafe)(int *);
 extern void (*cpu_setperf)(int);
 
 int net_ifiq_sysctl(int *, u_int, void *, size_t *, void *, size_t);