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c4a3af12fc
This is the same address that the x86_64 kernel runs at, and allows us to run the kernel at a high virtual memory address. Since we now run completely in high virtual memory, we can also unmap the identity mapping. Additionally some changes in MMU.cpp are required to successfully boot.
65 lines
2.1 KiB
C++
65 lines
2.1 KiB
C++
/*
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* Copyright (c) 2023, Timon Kruiper <timonkruiper@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/StringView.h>
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#include <AK/Types.h>
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#include <Kernel/Arch/aarch64/CPU.h>
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#include <Kernel/Sections.h>
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// We arrive here from boot.S with the MMU disabled and in an unknown exception level (EL).
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// The kernel is linked at the virtual address, so we have to be really carefull when accessing
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// global variables, as the MMU is not yet enabled.
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// FIXME: This should probably be shared with the Prekernel.
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namespace Kernel {
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extern "C" [[noreturn]] void init();
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extern "C" [[noreturn]] void pre_init();
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extern "C" [[noreturn]] void pre_init()
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{
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// We want to drop to EL1 as soon as possible, because that is the
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// exception level the kernel should run at.
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initialize_exceptions();
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// Next step is to set up page tables and enable the MMU.
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init_page_tables();
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// At this point the MMU is enabled, physical memory is identity mapped,
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// and the kernel is also mapped into higher virtual memory. However we are still executing
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// from the physical memory address, so we have to jump to the kernel in high memory. We also need to
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// switch the stack pointer to high memory, such that we can unmap the identity mapping.
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// Continue execution at high virtual address, by using an absolute jump.
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asm volatile(
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"ldr x0, =1f \n"
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"br x0 \n"
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"1: \n" ::
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: "x0");
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// Add kernel_mapping_base to the stack pointer, such that it is also using the mapping
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// in high virtual memory.
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asm volatile(
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"mov x0, %[base] \n"
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"add sp, sp, x0 \n" ::[base] "r"(kernel_mapping_base)
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: "x0");
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// We can now unmap the identity map as everything is running in high virtual memory at this point.
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unmap_identity_map();
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// Clear the frame pointer (x29) and link register (x30) to make sure the kernel cannot backtrace
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// into this code, and jump to actual init function in the kernel.
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asm volatile(
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"mov x29, xzr \n"
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"mov x30, xzr \n"
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"b init \n");
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VERIFY_NOT_REACHED();
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}
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}
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