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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@gmail.com> Cc: James Morse <james.morse@arm.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Marc Zyngier <maz@kernel.org> Cc: Mark Brown <broonie@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Remi Denis-Courmont <remi.denis.courmont@huawei.com> Cc: Ard Biesheuvel <ardb@kernel.org> 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 <will@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.