diff --git a/sys/arm64/arm64/sys_machdep.c b/sys/arm64/arm64/sys_machdep.c
--- a/sys/arm64/arm64/sys_machdep.c
+++ b/sys/arm64/arm64/sys_machdep.c
@@ -28,6 +28,7 @@
  */
 
 #include <sys/param.h>
+#include <sys/proc.h>
 #include <sys/systm.h>
 #include <sys/proc.h>
 #include <sys/sysproto.h>
@@ -36,14 +37,19 @@
 #include <vm/pmap.h>
 #include <vm/vm_map.h>
 
+#include <machine/pcb.h>
 #include <machine/sysarch.h>
 #include <machine/vmparam.h>
 
+#include <security/audit/audit.h>
+
 int
 sysarch(struct thread *td, struct sysarch_args *uap)
 {
 	struct arm64_guard_page_args gp_args;
+	struct pcb *pcb;
 	vm_offset_t eva;
+	unsigned long sve_len;
 	int error;
 
 	switch (uap->op) {
@@ -73,6 +79,13 @@
 		error = pmap_bti_set(vmspace_pmap(td->td_proc->p_vmspace),
 		    trunc_page(gp_args.addr), round_page(eva));
 		break;
+	case ARM64_GET_SVE_VL:
+		pcb = td->td_pcb;
+		sve_len = pcb->pcb_sve_len;
+		error = EINVAL;
+		if (sve_len != 0)
+			error = copyout(&sve_len, uap->parms, sizeof(sve_len));
+		break;
 	default:
 		error = EINVAL;
 		break;
diff --git a/sys/arm64/include/sysarch.h b/sys/arm64/include/sysarch.h
--- a/sys/arm64/include/sysarch.h
+++ b/sys/arm64/include/sysarch.h
@@ -46,6 +46,9 @@
 	__size_t	len;
 };
 
+#define	ARM64_GET_SVE_VL	0x200
+/* Reserved ARM64_SET_SVE_VL	0x201 */
+
 #ifndef _KERNEL
 
 __BEGIN_DECLS