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
@@ -28,14 +28,37 @@
  */
 
 #include <sys/param.h>
+#include <sys/proc.h>
 #include <sys/systm.h>
 #include <sys/sysproto.h>
 
+#include <machine/pcb.h>
 #include <machine/sysarch.h>
 
+#include <security/audit/audit.h>
+
 int
 sysarch(struct thread *td, struct sysarch_args *uap)
 {
+	struct pcb *pcb;
+	unsigned long sve_len;
+	int error;
+
+	pcb = td->td_pcb;
+
+	error = EINVAL;
+	AUDIT_ARG_CMD(uap->op);
+	switch (uap->op) {
+	case ARM64_GET_SVE_VL:
+		/* TODO: Check for SVE support */
+		sve_len = pcb->pcb_sve_len;
+		if (sve_len != 0)
+			error = copyout(&sve_len, uap->parms, sizeof(sve_len));
+		break;
+	default:
+		error = EINVAL;
+		break;
+	}
 
-	return (ENOTSUP);
+	return (error);
 }
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
@@ -39,6 +39,9 @@
 #ifndef _MACHINE_SYSARCH_H_
 #define	_MACHINE_SYSARCH_H_
 
+#define	ARM64_GET_SVE_VL	0x200
+/* Reserved ARM64_SET_SVE_VL	0x201 */
+
 #ifndef _KERNEL
 
 __BEGIN_DECLS