aedrix-kernel/arch/i386/kernel/mmu.c

/*
    Copyright (C) 2012, Aaron Lindsay <aaron@aclindsay.com>

    This file is part of Aedrix.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <print.h>
#include <types.h>

#include <arch/properties.h>

#define PAGE_SIZE 0x00400000
#define ROUND_DOWN_PAGE_SIZE(addr) ((typeof(addr))((uint32)(addr) & 0xff800000))

static inline int page_intersects(uint32 *page_start, uint32 *lower, uint32 *upper) {
	return (lower >= page_start && lower < (page_start + (PAGE_SIZE>>2))) ||
		(upper >= page_start && upper < (page_start + (PAGE_SIZE>>2))) ||
		(lower < page_start && upper >= (page_start + (PAGE_SIZE>>2)));
}

void mmu_reinit() {
	uint32 virt_phys_offset; /* CAUTION: 1 = 4 bytes */
	uint32 *curr_tbl_entry;
	uint32 *curr_addr;
	uint32 *page_dir;
	asm("movl %%cr3, %0" : "=r"(page_dir) : : );

	virt_phys_offset = kernel_start_virtual() - kernel_start_physical();
	curr_tbl_entry = page_dir + virt_phys_offset;

	//do first loop iteration outside th eloop, because we have to check against wrapping back around to know we're done
	*curr_tbl_entry = 0x83;
	curr_tbl_entry++;

	//create identity mapping for entire address space using sections.
	//BUT, if we've relocated the kernel from where it is in physical
	//memory, make sure we keep those mappings correct, and we'll actually
	//swap the two mappings so all of memory is addressable.
	for (curr_addr = (uint32 *)PAGE_SIZE; curr_addr != 0; curr_addr += (PAGE_SIZE>>2)) {
		if (page_intersects(curr_addr, kernel_start_physical(), kernel_end_physical())) {
			*curr_tbl_entry = (uint32)ROUND_DOWN_PAGE_SIZE(curr_addr + virt_phys_offset) | 0x83;
		} else if (page_intersects(curr_addr, kernel_start_virtual(), kernel_end_virtual())) {
			*curr_tbl_entry = (uint32)ROUND_DOWN_PAGE_SIZE(curr_addr - virt_phys_offset) | 0x83;
		} else {
			*curr_tbl_entry = (uint32)curr_addr | 0x83;
		}
		/* Force the entries to reload */
		asm("invlpg (%0)" : : "r"(curr_addr) : );
		curr_tbl_entry++;
	}
}