efi_loader: refactor switch to non-secure mode

Refactor the switch from supervisor to hypervisor to a new function called
at the beginning of do_bootefi().

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

2 files changed, 56 insertions, 0 deletions

diff --git a/arch/arm/cpu/armv8/Makefile b/arch/arm/cpu/armv8/Makefile
index 4c4b13c9e7..a5f54330e3 100644
--- a/arch/arm/cpu/armv8/Makefile
+++ b/arch/arm/cpu/armv8/Makefile
@@ -14,6 +14,7 @@ ifdef CONFIG_SPL_BUILD
 obj-$(CONFIG_ARMV8_SPL_EXCEPTION_VECTORS) += exceptions.o
 else
 obj-y	+= exceptions.o
+obj-y	+= exception_level.o
 endif
 obj-y	+= cache.o
 obj-y	+= tlb.o
diff --git a/arch/arm/cpu/armv8/exception_level.c b/arch/arm/cpu/armv8/exception_level.c
new file mode 100644
index 0000000000..57824eb2ac
--- /dev/null
+++ b/arch/arm/cpu/armv8/exception_level.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Switch to non-secure mode
+ *
+ * Copyright (c) 2018 Heinrich Schuchardt
+ *
+ * This module contains the ARMv8 specific code required to adjust the exception
+ * level before booting an operating system.
+ */
+
+#include <common.h>
+#include <bootm.h>
+#include <asm/setjmp.h>
+
+/**
+ * entry_non_secure() - entry point when switching to non-secure mode
+ *
+ * When switching to non-secure mode switch_to_non_secure_mode() calls this
+ * function passing a jump buffer. We use this jump buffer to restore the
+ * original stack and register state.
+ *
+ * @non_secure_jmp:	jump buffer for restoring stack and registers
+ */
+static void entry_non_secure(struct jmp_buf_data *non_secure_jmp)
+{
+	dcache_enable();
+	debug("Reached non-secure mode\n");
+
+	/* Restore stack and registers saved in switch_to_non_secure_mode() */
+	longjmp(non_secure_jmp, 1);
+}
+
+/**
+ * switch_to_non_secure_mode() - switch to non-secure mode
+ *
+ * Exception level EL3 is meant to be used by the secure monitor only (ARM
+ * trusted firmware being one embodiment). The operating system shall be
+ * started at exception level EL2. So here we check the exception level
+ * and switch it if necessary.
+ */
+void switch_to_non_secure_mode(void)
+{
+	struct jmp_buf_data non_secure_jmp;
+
+	/* On AArch64 we need to make sure we call our payload in < EL3 */
+	if (current_el() == 3) {
+		if (setjmp(&non_secure_jmp))
+			return;
+		dcache_disable();	/* flush cache before switch to EL2 */
+
+		/* Move into EL2 and keep running there */
+		armv8_switch_to_el2((uintptr_t)&non_secure_jmp, 0, 0, 0,
+				    (uintptr_t)entry_non_secure, ES_TO_AARCH64);
+	}
+}