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Kernel/aarch64: Ensure global variable accesses work without MMU enabled

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Since we link the kernel at a high virtual memory address, the addresses
of global variables are also at virtual addresses. To be able to access
them without the MMU enabled, we have to subtract the
KERNEL_MAPPING_BASE.
This commit is contained in:
Timon Kruiper 2023-01-07 10:44:01 +01:00 committed by Linus Groh
parent fdc687a911
commit 3bc122fcef
1 changed files with 19 additions and 7 deletions
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26
Kernel/Arch/aarch64/MMU.cpp
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@ -81,6 +81,18 @@ private:
};
}
// NOTE: To access global variables while the MMU is not yet enabled, we need
// to convert the address of a global variable to a physical address by
// subtracting KERNEL_MAPPING_BASE. This is because the kernel is linked
// for virtual memory at KERNEL_MAPPING_BASE, so a regular access to global variables
// will use the high virtual memory address. This does not work when the MMU is not yet
// enabled, so this function must be used for accessing global variables.
template<typename T>
inline T* adjust_by_mapping_base(T* ptr)
{
return (T*)((FlatPtr)ptr);
}
static u64* insert_page_table(PageBumpAllocator& allocator, u64* page_table, VirtualAddress virtual_addr)
{
// Each level has 9 bits (512 entries)
@ -132,7 +144,7 @@ static void setup_quickmap_page_table(PageBumpAllocator& allocator, u64* root_ta
{
// FIXME: Rename boot_pd_kernel_pt1023 to quickmap_page_table
// FIXME: Rename KERNEL_PT1024_BASE to quickmap_page_table_address
boot_pd_kernel_pt1023 = (PageTableEntry*)insert_page_table(allocator, root_table, VirtualAddress { KERNEL_PT1024_BASE });
*adjust_by_mapping_base(&boot_pd_kernel_pt1023) = (PageTableEntry*)insert_page_table(allocator, root_table, VirtualAddress { KERNEL_PT1024_BASE });
}
static void build_mappings(PageBumpAllocator& allocator, u64* root_table)
@ -221,26 +233,26 @@ static u64* get_page_directory(u64* root_table, VirtualAddress virtual_addr)
static void setup_kernel_page_directory(u64* root_table)
{
auto kernel_page_directory = (PhysicalPtr)get_page_directory(root_table, VirtualAddress { kernel_mapping_base });
auto kernel_page_directory = (PhysicalPtr)get_page_directory(root_table, VirtualAddress { *adjust_by_mapping_base(&kernel_mapping_base) });
if (!kernel_page_directory)
panic_without_mmu("Could not find kernel page directory!"sv);
boot_pd_kernel = PhysicalAddress(kernel_page_directory);
*adjust_by_mapping_base(&boot_pd_kernel) = PhysicalAddress(kernel_page_directory);
}
void init_page_tables()
{
// We currently identity map the physical memory, so the offset is 0.
physical_to_virtual_offset = 0;
kernel_mapping_base = 0;
*adjust_by_mapping_base(&physical_to_virtual_offset) = 0;
*adjust_by_mapping_base(&kernel_mapping_base) = 0;
PageBumpAllocator allocator((u64*)page_tables_phys_start, (u64*)page_tables_phys_end);
PageBumpAllocator allocator(adjust_by_mapping_base((u64*)page_tables_phys_start), adjust_by_mapping_base((u64*)page_tables_phys_end));
auto root_table = allocator.take_page();
build_mappings(allocator, root_table);
setup_quickmap_page_table(allocator, root_table);
setup_kernel_page_directory(root_table);
switch_to_page_table(page_tables_phys_start);
switch_to_page_table(adjust_by_mapping_base(page_tables_phys_start));
activate_mmu();
}