arm64: kernel: use literal for relocated address of __secondary_switched

We can simply use a relocated 64-bit literal to store the address of
__secondary_switched(), and the relocation code will ensure that it
holds the correct value at secondary entry time, as long as we make sure
that the literal is not dereferenced until after we have enabled the MMU.

So jump via a small __secondary_switch() function covered by the ID map
that performs the literal load and branch-to-register.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from commit e5ebeec879b726c755af0c1c15f3699b53268cd5)
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Author: Ard Biesheuvel

arch/arm64/kernel/head.S

@@ -466,9 +466,7 @@ __mmap_switched:
 	str	x15, [x11, x23]
 	b	0b
 
-2:	adr_l	x8, kimage_vaddr		// make relocated kimage_vaddr
-	dc	cvac, x8			// value visible to secondaries
-	dsb	sy				// with MMU off
+2:
 #endif
 
 	adr_l	sp, initial_sp, x4
@@ -672,12 +670,9 @@ secondary_startup:
 	adrp	x26, swapper_pg_dir
 	bl	__cpu_setup			// initialise processor
 
-	ldr	x8, kimage_vaddr
-	ldr	w9, 0f
-	sub	x27, x8, w9, sxtw		// address to jump to after enabling the MMU
+	adr_l	x27, __secondary_switch		// address to jump to after enabling the MMU
 	b	__enable_mmu
 ENDPROC(secondary_startup)
-0:	.long	(_text - TEXT_OFFSET) - __secondary_switched
 
 __secondary_switched:
 	adr_l	x5, vectors
@@ -750,3 +745,8 @@ __no_granule_support:
 	wfe
 	b __no_granule_support
 ENDPROC(__no_granule_support)
+
+__secondary_switch:
+	ldr	x8, =__secondary_switched
+	br	x8
+ENDPROC(__secondary_switch)