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Kernel: Unmap Prekernel pages after they are no longer needed

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The Prekernel's memory is only accessed until MemoryManager has been
initialized. Keeping them around afterwards is both unnecessary and bad,
as it prevents the userland from using the 0x100000-0x155000 virtual
address range.

Co-authored-by: Idan Horowitz <idan.horowitz@gmail.com>
This commit is contained in:
Daniel Bertalan 2021-12-19 01:15:12 +01:00 committed by Brian Gianforcaro
parent 2f1b4b8a81
commit 4fc28bfe02
Notes: sideshowbarker 2024-07-17 22:23:21 +09:00 
Author: https://github.com/BertalanD
Commit: https://github.com/SerenityOS/serenity/commit/4fc28bfe02f
Pull-request: https://github.com/SerenityOS/serenity/pull/11318
Reviewed-by: https://github.com/IdanHo
Reviewed-by: https://github.com/bgianfo ✅
4 changed files with 31 additions and 8 deletions
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20
Kernel/Memory/MemoryManager.cpp
View File

@ -106,6 +106,19 @@ UNMAP_AFTER_INIT void MemoryManager::protect_kernel_image()
}
}
UNMAP_AFTER_INIT void MemoryManager::unmap_prekernel()
{
SpinlockLocker page_lock(kernel_page_directory().get_lock());
SpinlockLocker mm_lock(s_mm_lock);
auto start = start_of_prekernel_image.page_base().get();
auto end = end_of_prekernel_image.page_base().get();
for (auto i = start; i <= end; i += PAGE_SIZE)
release_pte(kernel_page_directory(), VirtualAddress(i), i == end ? IsLastPTERelease::Yes : IsLastPTERelease::No, UnsafeIgnoreMissingPageTable::Yes);
flush_tlb(&kernel_page_directory(), VirtualAddress(start), (end - start) / PAGE_SIZE);
}
UNMAP_AFTER_INIT void MemoryManager::protect_readonly_after_init_memory()
{
SpinlockLocker page_lock(kernel_page_directory().get_lock());
@ -200,7 +213,6 @@ UNMAP_AFTER_INIT void MemoryManager::parse_memory_map()
// Register used memory regions that we know of.
m_used_memory_ranges.ensure_capacity(4);
m_used_memory_ranges.append(UsedMemoryRange { UsedMemoryRangeType::LowMemory, PhysicalAddress(0x00000000), PhysicalAddress(1 * MiB) });
m_used_memory_ranges.append(UsedMemoryRange { UsedMemoryRangeType::Prekernel, start_of_prekernel_image, end_of_prekernel_image });
m_used_memory_ranges.append(UsedMemoryRange { UsedMemoryRangeType::Kernel, PhysicalAddress(virtual_to_low_physical((FlatPtr)start_of_kernel_image)), PhysicalAddress(page_round_up(virtual_to_low_physical((FlatPtr)end_of_kernel_image))) });
if (multiboot_flags & 0x4) {
@ -570,7 +582,7 @@ PageTableEntry* MemoryManager::ensure_pte(PageDirectory& page_directory, Virtual
return &quickmap_pt(PhysicalAddress((FlatPtr)pde.page_table_base()))[page_table_index];
}
void MemoryManager::release_pte(PageDirectory& page_directory, VirtualAddress vaddr, bool is_last_release)
void MemoryManager::release_pte(PageDirectory& page_directory, VirtualAddress vaddr, IsLastPTERelease is_last_pte_release, UnsafeIgnoreMissingPageTable unsafe_ignore_missing_page_table)
{
VERIFY_INTERRUPTS_DISABLED();
VERIFY(s_mm_lock.is_locked_by_current_processor());
@ -586,7 +598,7 @@ void MemoryManager::release_pte(PageDirectory& page_directory, VirtualAddress va
auto& pte = page_table[page_table_index];
pte.clear();
if (is_last_release || page_table_index == 0x1ff) {
if (is_last_pte_release == IsLastPTERelease::Yes || page_table_index == 0x1ff) {
// If this is the last PTE in a region or the last PTE in a page table then
// check if we can also release the page table
bool all_clear = true;
@ -600,7 +612,7 @@ void MemoryManager::release_pte(PageDirectory& page_directory, VirtualAddress va
pde.clear();
auto result = page_directory.m_page_tables.remove(vaddr.get() & ~0x1fffff);
VERIFY(result);
VERIFY(unsafe_ignore_missing_page_table == UnsafeIgnoreMissingPageTable::Yes || result);
}
}
}

15
Kernel/Memory/MemoryManager.h
View File

@ -49,19 +49,19 @@ inline FlatPtr virtual_to_low_physical(FlatPtr virtual_)
enum class UsedMemoryRangeType {
LowMemory = 0,
Prekernel,
Kernel,
BootModule,
PhysicalPages,
__Count
};
static constexpr StringView UserMemoryRangeTypeNames[] {
"Low memory",
"Prekernel",
"Kernel",
"Boot module",
"Physical Pages"
};
static_assert(array_size(UserMemoryRangeTypeNames) == to_underlying(UsedMemoryRangeType::__Count));
struct UsedMemoryRange {
UsedMemoryRangeType type {};
@ -159,6 +159,7 @@ public:
void set_page_writable_direct(VirtualAddress, bool);
void protect_readonly_after_init_memory();
void unmap_prekernel();
void unmap_text_after_init();
void protect_ksyms_after_init();
@ -276,7 +277,15 @@ private:
PageTableEntry* pte(PageDirectory&, VirtualAddress);
PageTableEntry* ensure_pte(PageDirectory&, VirtualAddress);
void release_pte(PageDirectory&, VirtualAddress, bool);
enum class IsLastPTERelease {
Yes,
No
};
enum class UnsafeIgnoreMissingPageTable {
Yes,
No
};
void release_pte(PageDirectory&, VirtualAddress, IsLastPTERelease, UnsafeIgnoreMissingPageTable = UnsafeIgnoreMissingPageTable::No);
RefPtr<PageDirectory> m_kernel_page_directory;

2
Kernel/Memory/Region.cpp
View File

@ -243,7 +243,7 @@ void Region::unmap(ShouldDeallocateVirtualRange deallocate_range)
size_t count = page_count();
for (size_t i = 0; i < count; ++i) {
auto vaddr = vaddr_from_page_index(i);
MM.release_pte(*m_page_directory, vaddr, i == count - 1);
MM.release_pte(*m_page_directory, vaddr, i == count - 1 ? MemoryManager::IsLastPTERelease::Yes : MemoryManager::IsLastPTERelease::No);
}
MemoryManager::flush_tlb(m_page_directory, vaddr(), page_count());
if (deallocate_range == ShouldDeallocateVirtualRange::Yes) {

2
Kernel/init.cpp
View File

@ -193,6 +193,8 @@ extern "C" [[noreturn]] UNMAP_AFTER_INIT void init(BootInfo const& boot_info)
CommandLine::initialize();
Memory::MemoryManager::initialize(0);
MM.unmap_prekernel();
// Ensure that the safemem sections are not empty. This could happen if the linker accidentally discards the sections.
VERIFY(+start_of_safemem_text != +end_of_safemem_text);
VERIFY(+start_of_safemem_atomic_text != +end_of_safemem_atomic_text);