diff --git a/sys/arm64/arm64/genassym.c b/sys/arm64/arm64/genassym.c
--- a/sys/arm64/arm64/genassym.c
+++ b/sys/arm64/arm64/genassym.c
@@ -59,6 +59,8 @@
 ASSYM(PCB_ONFAULT, offsetof(struct pcb, pcb_onfault));
 ASSYM(PCB_FLAGS, offsetof(struct pcb, pcb_flags));
 
+ASSYM(PR_PID, offsetof(struct proc, p_pid));
+
 ASSYM(SF_UC, offsetof(struct sigframe, sf_uc));
 
 ASSYM(TD_PROC, offsetof(struct thread, td_proc));
diff --git a/sys/arm64/arm64/swtch.S b/sys/arm64/arm64/swtch.S
--- a/sys/arm64/arm64/swtch.S
+++ b/sys/arm64/arm64/swtch.S
@@ -55,6 +55,15 @@
 999:
 .endm
 
+.macro pid_in_context_idr label
+	adrp	x9, arm64_pid_in_contextidr
+	ldr	x10, [x9, :lo12:arm64_pid_in_contextidr]
+	cbz	x10, \label
+	ldr	x9, [x1, #TD_PROC]
+	ldr	x10, [x9, #PR_PID]
+	msr	contextidr_el1, x10
+.endm
+
 /*
  * void cpu_throw(struct thread *old, struct thread *new)
  */
@@ -66,8 +75,12 @@
 	ldr	x4, [x0, #TD_PCB]
 	ldr	w5, [x4, #PCB_FLAGS]
 	clear_step_flag w5, x6
+
 1:
+	/* debug/trace: set CONTEXTIDR_EL1 to current PID, if enabled */
+	pid_in_context_idr 2f
 
+2:
 #ifdef VFP
 	/* Backup the new thread pointer around a call to C code */
 	mov	x19, x1
@@ -147,6 +160,10 @@
 	mov	x20, x1
 	mov	x21, x2
 
+	/* debug/trace: set CONTEXTIDR_EL1 to current PID, if enabled */
+	pid_in_context_idr 0f
+
+0:
 #ifdef VFP
 	bl	vfp_save_state_switch
 	mov	x0, x20
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
@@ -30,6 +30,7 @@
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/proc.h>
+#include <sys/sysctl.h>
 #include <sys/sysproto.h>
 
 #include <vm/vm.h>
@@ -80,3 +81,8 @@
 
 	return (error);
 }
+
+bool arm64_pid_in_contextidr = false;
+SYSCTL_BOOL(_machdep, OID_AUTO, pid_in_contextidr, CTLFLAG_RW,
+    &arm64_pid_in_contextidr, false,
+    "Save PID into CONTEXTIDR_EL1 register on context switch");