[BOOT-WRAPPER 04/11] aarch64: Always enter kernel via exception return

[Mark Rutland]

When the boot-wrapper is entered at EL3 it will enter the kernel via
ERET, and when entered at EL2 it will branch to the kernel directly.
This is an artifact of the way the boot-wrapper was originally written
in assembly, and it would be preferable to always enter the kernel via
ERET so that PSTATE is always initialized to a known-good value.

Rework jump_kernel() to always enter the kernel via ERET.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Akos Denke <akos.denke at arm.com>
Cc: Andre Przywara <andre.przywara at arm.com>
Cc: Luca Fancellu <luca.fancellu at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
---
 arch/aarch64/boot.S | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S
index d8d38dd..3dbf85a 100644
--- a/arch/aarch64/boot.S
+++ b/arch/aarch64/boot.S
@@ -76,10 +76,6 @@ reset_at_el2:
 	b.eq	err_invalid_id
 	bl	setup_stack
 
-	mov	w0, #1
-	ldr	x1, =flag_no_el3
-	str	w0, [x1]
-
 	bl	cpu_init_bootwrapper
 
 	bl	cpu_init_arch
@@ -111,25 +107,26 @@ ASM_FUNC(jump_kernel)
 	bl	find_logical_id
 	bl	setup_stack		// Reset stack pointer
 
-	ldr	w0, flag_no_el3
-	cmp	w0, #0			// Prepare Z flag
-
 	mov	x0, x20
 	mov	x1, x21
 	mov	x2, x22
 	mov	x3, x23
+	mov	x4, #SPSR_KERNEL
 
-	b.eq	1f
-	br	x19			// No EL3
+	mrs	x5, CurrentEL
+	cmp	x5, #CURRENTEL_EL3
+	b.eq	eret_at_el3
+	cmp	x5, #CURRENTEL_EL2
+	b.eq	eret_at_el2
+	b	.			// Not possible
 
-1:	mov	x4, #SPSR_KERNEL
+eret_at_el3:
 	msr	elr_el3, x19
 	msr	spsr_el3, x4
 	eret
+eret_at_el2:
+	msr	elr_el2, x19
+	msr	spsr_el2, x4
+	eret
 
 	.ltorg
-
-	.data
-	.align 3
-flag_no_el3:
-	.long 0
-- 
2.30.2