Gabriel
c4bb857c4e
In the kernel's early stages we access physical memory identity-mapped, so it's not very good for us to allocate that frame and then try to use it.
107 lines
3.7 KiB
Zig
107 lines
3.7 KiB
Zig
const std = @import("std");
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const easyboot = @cImport(@cInclude("easyboot.h"));
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const platform = @import("arch/platform.zig").arch;
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const mmap = @import("mmap.zig");
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const bmap = @import("lib/bitmap.zig");
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const FrameAllocatorError = error{
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InvalidMemoryMap,
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MemoryAlreadyInUse,
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MemoryNotInUse,
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OutOfMemory,
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};
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pub const FrameAllocator = struct {
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bitmap: bmap.Bitmap,
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free_memory: u64,
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used_memory: u64,
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reserved_memory: u64,
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start_index: usize,
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};
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pub const PhysFrame = struct {
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address: usize,
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pub fn virtualAddress(self: *const PhysFrame, base: usize) usize {
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return base + self.address;
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}
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};
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pub fn lockFrame(allocator: *FrameAllocator, address: usize) !void {
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const index = address / platform.PAGE_SIZE;
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if (try allocator.bitmap.get(index) == 1) return error.MemoryAlreadyInUse;
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try allocator.bitmap.set(index, 1);
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allocator.used_memory += platform.PAGE_SIZE;
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allocator.free_memory -= platform.PAGE_SIZE;
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}
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pub fn lockFrames(allocator: *FrameAllocator, address: usize, pages: usize) !void {
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var index: usize = 0;
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while (index < pages) : (index += 1) {
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try lockFrame(allocator, address + (index * platform.PAGE_SIZE));
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}
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}
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pub fn freeFrame(allocator: *FrameAllocator, address: usize) !void {
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const index = address / platform.PAGE_SIZE;
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if (try allocator.bitmap.get(index) == 0) return error.MemoryNotInUse;
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try allocator.bitmap.set(index, 0);
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allocator.used_memory -= platform.PAGE_SIZE;
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allocator.free_memory += platform.PAGE_SIZE;
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if (allocator.start_index > index) allocator.start_index = index;
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}
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pub fn freeFrames(allocator: *FrameAllocator, address: usize, pages: usize) !void {
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const index: usize = 0;
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while (index < pages) : (index += 1) {
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try freeFrame(allocator, address + (index * platform.PAGE_SIZE));
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}
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}
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pub fn allocFrame(allocator: *FrameAllocator) !PhysFrame {
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const index: usize = try bmap.findInBitmap(&allocator.bitmap, 0, allocator.start_index) orelse return error.OutOfMemory;
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const address = index * platform.PAGE_SIZE;
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try lockFrame(allocator, address);
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allocator.start_index = index + 1;
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return PhysFrame{ .address = address };
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}
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pub fn initializeFrameAllocator(tag: *easyboot.multiboot_tag_mmap_t) !FrameAllocator {
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const largest_free = mmap.findLargestFreeEntry(tag) orelse return error.InvalidMemoryMap;
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const physical_address_space_size = mmap.getAddressSpaceSize(tag) orelse return error.InvalidMemoryMap;
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const bitmap_base_address: [*]u8 = @ptrFromInt(largest_free.base_addr);
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const bitmap_bit_size = physical_address_space_size / @as(usize, platform.PAGE_SIZE);
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const bitmap_size: usize = try std.math.divCeil(usize, bitmap_bit_size, 8);
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var allocator: FrameAllocator = FrameAllocator{ .bitmap = bmap.createBitmap(bitmap_base_address, bitmap_size), .free_memory = 0, .used_memory = 0, .reserved_memory = 0, .start_index = 0 };
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allocator.bitmap.clear(1); // Set all pages to used/reserved by default, then clear out the free ones
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var iter = mmap.createMemoryMapIterator(tag);
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while (iter.next()) |entry| {
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const index = entry.base_addr / platform.PAGE_SIZE;
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const pages = entry.length / platform.PAGE_SIZE;
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if (entry.type != easyboot.MULTIBOOT_MEMORY_AVAILABLE) {
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allocator.reserved_memory += entry.length;
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continue;
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}
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allocator.free_memory += entry.length;
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try bmap.updateBitmapRegion(&allocator.bitmap, index, pages, 0);
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}
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const frames_to_lock = try std.math.divCeil(usize, bitmap_size, platform.PAGE_SIZE);
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try lockFrames(&allocator, @intFromPtr(bitmap_base_address), frames_to_lock);
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// Avoid causing trouble.
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try lockFrame(&allocator, 0);
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return allocator;
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}
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