From 995d1bc36e1323c75ddaad25741c5e2afbdb9618 Mon Sep 17 00:00:00 2001 From: apio Date: Mon, 27 Feb 2023 12:24:21 +0100 Subject: [PATCH] x86_64/MMU: Map all physical memory into the higher half instead of using recursive mapping This still has a few problems. Notably, we are not using huge pages for this mapping, which would be a lot more efficient. Right now, used memory is 8.1 MiB at boot for a 256MiB system. But after improving it, this system will be much better than recursive mapping. fork() will be MUCH easier to implement, for example. --- kernel/src/arch/x86_64/MMU.cpp | 225 +++++++++++++++------------------ 1 file changed, 99 insertions(+), 126 deletions(-) diff --git a/kernel/src/arch/x86_64/MMU.cpp b/kernel/src/arch/x86_64/MMU.cpp index 2bd6ee49..2f85f238 100644 --- a/kernel/src/arch/x86_64/MMU.cpp +++ b/kernel/src/arch/x86_64/MMU.cpp @@ -1,6 +1,8 @@ #include "arch/MMU.h" #include "Log.h" #include "memory/MemoryManager.h" +#include "memory/MemoryMap.h" +#include #include #include #include @@ -12,6 +14,10 @@ PageDirectory* g_kernel_directory; u64 g_kernel_directory_virt; +// The bootloader maps up to 16GiB of physical memory for us at address 0. Using this bootstrap mapping, we'll map (all) +// physical memory at 0xFFFF800000000000. +u64 g_physical_mapping_base = 0; + void PageTableEntry::set_address(u64 addr) { this->address = (addr >> 12); @@ -36,90 +42,9 @@ static bool has_flag(int flags, MMU::Flags flag) namespace MMU { - - constexpr PageDirectory* l4_table() + template T translate_physical(T phys) { - constexpr u64 l4 = sign | (rindex << 39) | (rindex << 30) | (rindex << 21) | (rindex << 12); - return (PageDirectory*)l4; - } - - constexpr u64 l4_index(u64 addr) - { - return (addr >> 39) & 0777; - } - - PageTableEntry& l4_entry(u64 addr) - { - return l4_table()->entries[l4_index(addr)]; - } - - constexpr PageDirectory* raw_l3_table(u64 l4) - { - const u64 l3 = sign | (rindex << 39) | (rindex << 30) | (rindex << 21) | (l4 << 12); - return (PageDirectory*)l3; - } - - constexpr PageDirectory* l3_table(u64 addr) - { - const u64 l4 = l4_index(addr); - return raw_l3_table(l4); - } - - constexpr u64 l3_index(u64 addr) - { - return (addr >> 30) & 0777; - } - - PageTableEntry& l3_entry(u64 addr) - { - return l3_table(addr)->entries[l3_index(addr)]; - } - - constexpr PageDirectory* raw_l2_table(u64 l4, u64 l3) - { - const u64 l2 = sign | (rindex << 39) | (rindex << 30) | (l4 << 21) | (l3 << 12); - return (PageDirectory*)l2; - } - - constexpr PageDirectory* l2_table(u64 addr) - { - const u64 l4 = l4_index(addr); - const u64 l3 = l3_index(addr); - return raw_l2_table(l4, l3); - } - - constexpr u64 l2_index(u64 addr) - { - return (addr >> 21) & 0777; - } - - PageTableEntry& l2_entry(u64 addr) - { - return l2_table(addr)->entries[l2_index(addr)]; - } - - constexpr PageDirectory* raw_l1_table(u64 l4, u64 l3, u64 l2) - { - const u64 l1 = sign | (rindex << 39) | (l4 << 30) | (l3 << 21) | (l2 << 12); - return (PageDirectory*)l1; - } - - constexpr PageDirectory* l1_table(u64 addr) - { - const u64 l4 = l4_index(addr); - const u64 l3 = l3_index(addr); - const u64 l2 = l2_index(addr); - return raw_l1_table(l4, l3, l2); - } - - constexpr u64 l1_index(u64 addr) - { - return (addr >> 12) & 0777; - } - - PageTableEntry& l1_entry(u64 addr) - { - return l1_table(addr)->entries[l1_index(addr)]; + return (T)(g_physical_mapping_base + (u64)phys); } void switch_page_directory(PageDirectory* dir) @@ -134,6 +59,11 @@ namespace MMU return value; } + PageDirectory* get_virtual_page_directory() + { + return translate_physical(get_page_directory()); + } + void flush_all() { switch_page_directory(get_page_directory()); @@ -144,6 +74,26 @@ namespace MMU asm volatile("invlpg (%0)" : : "r"(page) : "memory"); } + constexpr u64 l4_index(u64 addr) + { + return (addr >> 39) & 0777; + } + + constexpr u64 l3_index(u64 addr) + { + return (addr >> 30) & 0777; + } + + constexpr u64 l2_index(u64 addr) + { + return (addr >> 21) & 0777; + } + + constexpr u64 l1_index(u64 addr) + { + return (addr >> 12) & 0777; + } + int arch_flags_to_mmu(const PageTableEntry& entry) { int result = Flags::None; @@ -155,17 +105,46 @@ namespace MMU return result; } + PageTableEntry& l4_entry(u64 virt) + { + auto index = l4_index(virt); + return get_virtual_page_directory()->entries[index]; + } + + PageDirectory& page_table(const PageTableEntry& entry) + { + return *translate_physical((PageDirectory*)entry.get_address()); + } + + PageTableEntry& l3_entry(const PageTableEntry& entry, u64 virt) + { + auto index = l3_index(virt); + return page_table(entry).entries[index]; + } + + PageTableEntry& l2_entry(const PageTableEntry& entry, u64 virt) + { + auto index = l2_index(virt); + return page_table(entry).entries[index]; + } + + PageTableEntry& l1_entry(const PageTableEntry& entry, u64 virt) + { + auto index = l1_index(virt); + return page_table(entry).entries[index]; + } + Result find_entry(u64 virt) { const auto& l4 = l4_entry(virt); if (!l4.present) return err(EFAULT); - auto& l3 = l3_entry(virt); + auto& l3 = l3_entry(l4, virt); if (!l3.present) return err(EFAULT); if (l3.larger_pages) return &l3; - auto& l2 = l2_entry(virt); + auto& l2 = l2_entry(l3, virt); if (!l2.present) return err(EFAULT); if (l2.larger_pages) return &l2; - return &l1_entry(virt); + return &l1_entry(l2, virt); } Result apply_cascading_flags(u64 virt, int flags) @@ -174,17 +153,17 @@ namespace MMU if (!l4.present) return err(EFAULT); if (flags & Flags::ReadWrite) l4.read_write = true; if (flags & Flags::User) l4.user = true; - auto& l3 = l3_entry(virt); + auto& l3 = l3_entry(l4, virt); if (!l3.present) return err(EFAULT); if (l3.larger_pages) return &l3; if (flags & Flags::ReadWrite) l3.read_write = true; if (flags & Flags::User) l3.user = true; - auto& l2 = l2_entry(virt); + auto& l2 = l2_entry(l3, virt); if (!l2.present) return err(EFAULT); if (l2.larger_pages) return &l2; if (flags & Flags::ReadWrite) l2.read_write = true; if (flags & Flags::User) l2.user = true; - auto& l1 = l1_entry(virt); + auto& l1 = l1_entry(l2, virt); return &l1; } @@ -196,38 +175,38 @@ namespace MMU const u64 addr = TRY(MemoryManager::alloc_frame()); l4.present = true; l4.set_address(addr); - memset(l3_table(virt), 0, ARCH_PAGE_SIZE); + memset(&page_table(l4), 0, ARCH_PAGE_SIZE); } if (flags & Flags::ReadWrite) l4.read_write = true; if (flags & Flags::User) l4.user = true; - auto& l3 = l3_entry(virt); + auto& l3 = l3_entry(l4, virt); if (!l3.present) { const u64 addr = TRY(MemoryManager::alloc_frame()); l3.present = true; l3.set_address(addr); - memset(l2_table(virt), 0, ARCH_PAGE_SIZE); + memset(&page_table(l3), 0, ARCH_PAGE_SIZE); } if (flags & Flags::ReadWrite) l3.read_write = true; if (flags & Flags::User) l3.user = true; if (l3.larger_pages) return err(EFIXME); // FIXME: Replacing larger pages is not supported ATM - auto& l2 = l2_entry(virt); + auto& l2 = l2_entry(l3, virt); if (!l2.present) { const u64 addr = TRY(MemoryManager::alloc_frame()); l2.present = true; l2.set_address(addr); - memset(l1_table(virt), 0, ARCH_PAGE_SIZE); + memset(&page_table(l2), 0, ARCH_PAGE_SIZE); } if (flags & Flags::ReadWrite) l2.read_write = true; if (flags & Flags::User) l2.user = true; if (l2.larger_pages) return err(EFIXME); // FIXME: Replacing larger pages is not supported ATM - auto& l1 = l1_entry(virt); + auto& l1 = l1_entry(l2, virt); if (l1.present) return err(EEXIST); // Please explicitly unmap the page before mapping it again. l1.present = true; l1.read_write = has_flag(flags, Flags::ReadWrite); @@ -281,39 +260,38 @@ namespace MMU PageDirectory* const dir = get_page_directory(); g_kernel_directory = dir; - const u64 paddr = (u64)dir; - PageTableEntry& recursive_entry = dir->entries[rindex]; - recursive_entry.read_write = true; - recursive_entry.present = true; - recursive_entry.set_address(paddr); - flush_all(); + const u64 physical_memory_base = 0xFFFF800000000000; - g_kernel_directory_virt = - MemoryManager::get_kernel_mapping_for_frames((u64)dir, 1, MMU::ReadWrite | MMU::NoExecute).value(); + MemoryMapIterator iter; + const MemoryMapEntry highest_entry = iter.highest(); + + const u64 physical_memory_size = highest_entry.address() + highest_entry.size(); + + // FIXME: Do this using 2MiB huge pages. + MemoryManager::map_frames_at(physical_memory_base, 0, physical_memory_size / ARCH_PAGE_SIZE, + MMU::ReadWrite | MMU::NoExecute); + + g_physical_mapping_base = physical_memory_base; + + g_kernel_directory_virt = translate_physical((u64)g_kernel_directory); kdbgln("MMU init page directory (ring0): virt %#.16lx, phys %p", g_kernel_directory_virt, g_kernel_directory); } Result create_page_directory_for_userspace() { - const u64 directory_virt = TRY(MemoryManager::alloc_for_kernel(1, MMU::ReadWrite | MMU::NoExecute)); - const u64 directory_phys = MMU::get_physical(directory_virt).value(); + const u64 directory_phys = TRY(MemoryManager::alloc_frame()); + const u64 directory_virt = translate_physical(directory_phys); PageDirectory* const directory = (PageDirectory*)directory_virt; memset(directory, 0, ARCH_PAGE_SIZE); - PageTableEntry& recursive_entry = directory->entries[rindex]; - recursive_entry.read_write = true; - recursive_entry.present = true; - recursive_entry.set_address(directory_phys); + + constexpr auto HALF_PAGE = ARCH_PAGE_SIZE / 2; + // Copy the upper part of the page directory (higher half) + memcpy(offset_ptr(directory, HALF_PAGE), offset_ptr(g_kernel_directory, HALF_PAGE), HALF_PAGE); kdbgln("MMU init page directory (ring3): virt %p, phys %#.16lx", directory, directory_phys); - directory->entries[511] = ((PageDirectory*)g_kernel_directory_virt)->entries[511]; - - // From now on, we're only going to use the physical address, since accessing the PageDirectory will be dealt - // with using recursive mapping. So let's make sure we don't leak any VM. - MemoryManager::unmap_weak_and_free_vm(directory_virt, 1); - return (PageDirectory*)directory_phys; } @@ -321,16 +299,11 @@ namespace MMU { check(directory); - // Needed in order to access page tables using the recursive mapping system. - switch_page_directory(directory); + switch_page_directory(g_kernel_directory); - auto guard = make_scope_guard([&] { - check(g_kernel_directory); - switch_page_directory(g_kernel_directory); - MemoryManager::free_frame((u64)directory); - }); + auto guard = make_scope_guard([directory] { MemoryManager::free_frame((u64)directory); }); - PageDirectory* const table = l4_table(); + PageDirectory* const table = translate_physical(directory); // Let's iterate over every top-level entry, skipping the last two entries (recursive mapping and kernel pages) for (u64 i = 0; i < 510; i++) @@ -338,7 +311,7 @@ namespace MMU PageTableEntry& l4 = table->entries[i]; if (!l4.present) continue; - PageDirectory* const pdp = raw_l3_table(i); + PageDirectory* const pdp = &page_table(l4); for (u64 j = 0; j < 512; j++) { @@ -350,7 +323,7 @@ namespace MMU TRY(MemoryManager::free_frame(l3.get_address())); } - PageDirectory* const pd = raw_l2_table(i, j); + PageDirectory* const pd = &page_table(l3); for (u64 k = 0; k < 512; k++) { @@ -362,7 +335,7 @@ namespace MMU TRY(MemoryManager::free_frame(l2.get_address())); } - PageDirectory* const pt = raw_l1_table(i, j, k); + PageDirectory* const pt = &page_table(l2); for (u64 l = 0; l < 512; l++) {