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 <kernelfans@xxxxxxxxx> Cc: James Morse <james.morse@xxxxxxx> Cc: Geoff Levand <geoff@xxxxxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Cc: Marc Zyngier <maz@xxxxxxxxxx> Cc: Mark Brown <broonie@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Remi Denis-Courmont <remi.denis.courmont@xxxxxxxxxx> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx --- 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 _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
