From 50864eda021b97534697e4d7374ccbcaa519e142 Mon Sep 17 00:00:00 2001
From: Travis Geiselbrecht <geist@foobox.com>
Date: Tue, 14 Oct 2025 00:45:03 -0700
Subject: [PATCH] [arch][arm64] add routine to read the boot EL

---
 arch/arm64/arch.c               |  9 +++++++++
 arch/arm64/include/arch/arm64.h | 11 +++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/arm64/arch.c b/arch/arm64/arch.c
index 6af6d993..aee19772 100644
--- a/arch/arm64/arch.c
+++ b/arch/arm64/arch.c
@@ -25,6 +25,9 @@
 
 #define LOCAL_TRACE 0
 
+/* Defined in start.S. */
+extern uint64_t arm64_boot_el;
+
 // initial setup per cpu immediately after entering C code
 void arm64_early_init_percpu(void) {
     // set the vector base
@@ -76,6 +79,12 @@ void arch_early_init(void) {
 // called after the kernel has been initialized and threading is enabled on the boot cpu
 void arch_init(void) {
     arm64_mp_init();
+
+    dprintf(INFO, "ARM64: boot EL%llu\n", arm64_get_boot_el());
+}
+
+uint64_t arm64_get_boot_el(void) {
+    return arm64_boot_el >> 2;
 }
 
 void arch_quiesce(void) {
diff --git a/arch/arm64/include/arch/arm64.h b/arch/arm64/include/arch/arm64.h
index a7c56fcb..5b9caf53 100644
--- a/arch/arm64/include/arch/arm64.h
+++ b/arch/arm64/include/arch/arm64.h
@@ -34,6 +34,8 @@ __BEGIN_CDECLS
 
 void arm64_context_switch(vaddr_t *old_sp, vaddr_t new_sp);
 
+uint64_t arm64_get_boot_el(void);
+
 /* exception handling */
 struct arm64_iframe_long {
     uint64_t r[30];
@@ -81,5 +83,14 @@ void arm64_local_invalidate_cache_all(void);
 void arm64_local_clean_invalidate_cache_all(void);
 void arm64_local_clean_cache_all(void);
 
+/* Current Exception Level values, as contained in CurrentEL */
+#define CurrentEL_EL1    (1 << 2)
+#define CurrentEL_EL2    (2 << 2)
+
+static inline bool arm64_is_kernel_in_hyp_mode(void) {
+    return ARM64_READ_SYSREG(CURRENTEL) == CurrentEL_EL2;
+}
+
+
 __END_CDECLS