From 72789a4a6a914601912a8992b0d43bd5abc05128 Mon Sep 17 00:00:00 2001 From: Pingfan Liu Date: Fri, 28 Aug 2020 21:39:57 +0800 Subject: [PATCH] arm64/relocate_kernel: remove redundant code Kernel startup entry point requires disabling MMU and D-cache. As for kexec-reboot, taking a close look at "msr sctlr_el1, x12" in __cpu_soft_restart as the following: -1. booted at EL1 The instruction is enough to disable MMU and I/D cache for EL1 regime. -2. booted at EL2, using VHE Access to SCTLR_EL1 is redirected to SCTLR_EL2 in EL2. So the instruction is enough to disable MMU and clear I+C bits for EL2 regime. -3. booted at EL2, not using VHE The instruction itself can not affect EL2 regime. But The hyp-stub doesn't enable the MMU and I/D cache for EL2 regime. And KVM also disable them for EL2 regime when its unloaded, or execute a HVC_SOFT_RESTART call. So when kexec-reboot, the code in KVM has prepare the requirement. As a conclusion, disabling MMU and clearing I+C bits in SYM_CODE_START(arm64_relocate_new_kernel) is redundant, and can be removed Signed-off-by: Pingfan Liu Cc: James Morse Cc: Geoff Levand Cc: Catalin Marinas Cc: Will Deacon Cc: Mark Rutland Cc: Marc Zyngier Cc: Mark Brown Cc: Kees Cook Cc: Remi Denis-Courmont Cc: Ard Biesheuvel Cc: kvmarm@lists.cs.columbia.edu Link: https://lore.kernel.org/r/1598621998-20563-1-git-send-email-kernelfans@gmail.com To: linux-arm-kernel@lists.infradead.org Signed-off-by: Will Deacon --- 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 4a18055b2ff9..37721eb6f9a1 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 542d6edc6806..84eec95ec06c 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