[PATCH] arm64/relocate_kernel: remove redundant but misleading code

[Pingfan Liu]

The kexec switch sequence looks like the following:
  SYM_CODE_START(__cpu_soft_restart)
    ...
    pre_disable_mmu_workaround
    msr	sctlr_el1, x12
    ...
    br	x8

  SYM_CODE_START(arm64_relocate_new_kernel)
    ...
    pre_disable_mmu_workaround
    msr	sctlr_el2, x0
    ...

"msr sctlr_el2, x0" is misleading, because "br x8" jump to a physical
address, which has no entry in idmap. It implies that MMU has already been
fully off after "msr sctlr_el1, x12".

And according to "D12.2.101 SCTLR_EL2, System Control Register (EL2)" in
"ARM Architecture Reference Manual", actually, EL2&0 host accesses
to SCTLR_EL2 when using mnemonic SCTLR_EL1.

Hence removing the redundant but misleading code.

Signed-off-by: Pingfan Liu <kernelfans at gmail.com>
Cc: Geoff Levand <geoff at infradead.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Mark Brown <broonie at kernel.org>
Cc: Kees Cook <keescook at chromium.org>
Cc: Remi Denis-Courmont <remi.denis.courmont at huawei.com>
Cc: Ard Biesheuvel <ardb at kernel.org>
To: linux-arm-kernel at lists.infradead.org
---
 arch/arm64/kernel/cpu-reset.S       |  4 ++++
 arch/arm64/kernel/relocate_kernel.S | 12 ------------
 2 files changed, 4 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kernel/cpu-reset.S b/arch/arm64/kernel/cpu-reset.S
index 4a18055..37721eb 100644
--- a/arch/arm64/kernel/cpu-reset.S
+++ b/arch/arm64/kernel/cpu-reset.S
@@ -35,6 +35,10 @@ SYM_CODE_START(__cpu_soft_restart)
 	mov_q	x13, SCTLR_ELx_FLAGS
 	bic	x12, x12, x13
 	pre_disable_mmu_workaround
+	/*
+	 * either disable EL1&0 translation regime or disable EL2&0 translation
+	 * regime if HCR_EL2.E2H == 1
+	 */
 	msr	sctlr_el1, x12
 	isb
 
diff --git a/arch/arm64/kernel/relocate_kernel.S b/arch/arm64/kernel/relocate_kernel.S
index 542d6ed..84eec95 100644
--- a/arch/arm64/kernel/relocate_kernel.S
+++ b/arch/arm64/kernel/relocate_kernel.S
@@ -36,18 +36,6 @@ SYM_CODE_START(arm64_relocate_new_kernel)
 	mov	x14, xzr			/* x14 = entry ptr */
 	mov	x13, xzr			/* x13 = copy dest */
 
-	/* Clear the sctlr_el2 flags. */
-	mrs	x0, CurrentEL
-	cmp	x0, #CurrentEL_EL2
-	b.ne	1f
-	mrs	x0, sctlr_el2
-	mov_q	x1, SCTLR_ELx_FLAGS
-	bic	x0, x0, x1
-	pre_disable_mmu_workaround
-	msr	sctlr_el2, x0
-	isb
-1:
-
 	/* Check if the new image needs relocation. */
 	tbnz	x16, IND_DONE_BIT, .Ldone
 
-- 
2.7.5