[PATCH v2 07/14] arm64: head: Force little-endian early during boot

[Will Deacon]

Commit 2ced0f30a426 ("arm64: head: Switch endianness before populating
the ID map") configured SCTLR_ELx.EE at boot according to the endianness
of the kernel in case the bootloader had entered the image in the wrong
endianness. Additionally, if the MMU was enabled in such a case, logic
was added to turn it back off to prevent the hardware walker from
misinterpreting the idmap page-table.

Given that the MMU is only expected to be enabled when booting EFI, EFI
only supports little-endian and arm64 kernels cannot be built as
big-endian images, we can rip out this handling and simply force
SCTLR_ELx.EE to 0 (little-endian).

Suggested-by: Ard Biesheuvel <ardb at kernel.org>
Signed-off-by: Will Deacon <will at kernel.org>
---
 arch/arm64/kernel/head.S | 20 +-------------------
 1 file changed, 1 insertion(+), 19 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 8951ce693552..d5c1ea0c5b3c 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -138,29 +138,11 @@ SYM_CODE_START_LOCAL(record_mmu_state)
 	b.ne	0f
 	mrs	x19, sctlr_el2
 0:
-	tbnz	x19, #SCTLR_ELx_EE_SHIFT, 1f
+	bic	x19, x19, #SCTLR_ELx_EE		// Force little-endian
 	tst	x19, #SCTLR_ELx_C		// Z := (C == 0)
 	and	x19, x19, #SCTLR_ELx_M		// isolate M bit
 	csel	x19, xzr, x19, eq		// clear x19 if Z
 	ret
-
-	/*
-	 * Set the correct endianness early so all memory accesses issued
-	 * before init_kernel_el() occur in the correct byte order. Note that
-	 * this means the MMU must be disabled, or the active ID map will end
-	 * up getting interpreted with the wrong byte order.
-	 */
-1:	eor	x19, x19, #SCTLR_ELx_EE
-	bic	x19, x19, #SCTLR_ELx_M
-	b.ne	2f
-	pre_disable_mmu_workaround
-	msr	sctlr_el2, x19
-	b	3f
-2:	pre_disable_mmu_workaround
-	msr	sctlr_el1, x19
-3:	isb
-	mov	x19, xzr
-	ret
 SYM_CODE_END(record_mmu_state)
 
 /*
-- 
2.55.0.979.g7e5102b832-goog