[RFC PATCH 6/8] arm64: head: clean the ID map page to the PoC

[Ard Biesheuvel]

If we enter with the MMU and caches enabled, the caller may not have
performed any cache maintenance. So clean the ID mapped page to the PoC,
and invalidate the I-cache so we can safely execute from it after
disabling the MMU and caches.

Note that this means primary_entry() itself needs to be moved into the
ID map as well, as we will return from init_kernel_el() with the MMU and
caches off.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/kernel/head.S | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 6041078df62a..ebc04d25f775 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -75,7 +75,7 @@
 
 	__EFI_PE_HEADER
 
-	__INIT
+	.section ".idmap.text","awx"
 
 	/*
 	 * The following callee saved general purpose registers are used on the
@@ -94,6 +94,19 @@ SYM_CODE_START(primary_entry)
 	bl	record_kaslr_offset
 	bl	preserve_boot_args
 	bl	__create_page_tables
+
+	/*
+	 * If we entered with the MMU and caches on, clean the ID mapped part
+	 * of the primary boot code to the PoC and invalidate it from the
+	 * I-cache so we can safely disable them.
+	 */
+	cbz	x25, 0f
+	adrp	x0, __idmap_text_start
+	adr_l	x1, __idmap_text_end
+	sub	x1, x1, x0
+	bl	dcache_clean_poc
+	ic	ialluis
+0:
 	bl	init_kernel_el			// w0=cpu_boot_mode
 	bl	set_cpu_boot_mode_flag
 	/*
@@ -106,6 +119,7 @@ SYM_CODE_START(primary_entry)
 	b	__primary_switch
 SYM_CODE_END(primary_entry)
 
+	__INIT
 SYM_CODE_START_LOCAL(record_mmu_state)
 	mrs	x25, CurrentEL
 	cmp	x25, #CurrentEL_EL2
-- 
2.30.2