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 <frames.h>

extern uint32 kernel_start_phys, kernel_end_phys;
extern uint32 kernel_start, kernel_end;

#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)) ||
		(upper >= page_start && upper < (page_start + PAGE_SIZE)) ||
		(lower < page_start && upper >= (page_start + PAGE_SIZE));
}

void mmu_reinit() {
	int 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 - &kernel_start_phys;
	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_phys, &kernel_end_phys)) {
			*curr_tbl_entry = (uint32)ROUND_DOWN_PAGE_SIZE(curr_addr + virt_phys_offset) | 0x83;
		} else if (page_intersects(curr_addr, &kernel_start, &kernel_end)) {
			*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++;
	}
}

//TODO merge the rest of this file with the similar section in arch/arm. This is clearly mostly duplicated code.

int mmu_region_contains(void *lower_a, void *upper_a, void *lower_b, void *upper_b) {
	return lower_b >= lower_a && upper_b <= upper_a;
}
int mmu_region_contains_single(void *lower_a, void *upper_a, void *ptr) {
	return lower_a <= ptr && ptr <= upper_a;
}

#define section_round_down(ptr) (((uint32)ptr) & ~(PAGE_SIZE-1))
#define section_round_up(ptr) (((((uint32)ptr) & ~1) + (PAGE_SIZE-1) ) & ~(PAGE_SIZE-1))

/* Called once per physical memory region by bootup code. This function is
 * responsible for only adding (via mm_add_free_region()) those parts of the
 * memory region which are still available (i.e. aren't in the kernel and
 * haven't been remapped anywhere else. */
void declare_memory_region(void *lower, void *upper) {
	void *k_section_start_phys = (void *)section_round_down(&kernel_start_phys);
	void *k_section_end_phys = (void *)(section_round_up(&kernel_end_phys) - 1);
	void *k_section_start_virt = (void *)section_round_down(&kernel_start);
	void *k_section_end_virt = (void *)(section_round_up(&kernel_end) - 1);

	if (upper - lower < 1) {
		print("Warning: declare_memory_region() called with lower=%x, upper=%x. Ignoring.\n", lower, upper);
		return;
	}

	//TODO It's possible (though highly unlikely) that the kernel (virtual)
	//is split across two different memory regions. We should probably
	//handle this.
	if (mmu_region_contains(lower, upper, k_section_start_phys, k_section_end_phys)) {
		//Don't map any of the physical kernel's memory
		declare_memory_region(lower, (void *) ((char *)k_section_start_phys - 1));
		declare_memory_region((void *) ((char *)k_section_end_phys + 1), upper);
		mm_add_free_region(&kernel_end, k_section_end_virt);
	} else if (mmu_region_contains(lower, upper, k_section_start_virt, k_section_end_virt)) {
		declare_memory_region(lower, (void *) ((char *)k_section_start_virt - 1));
		declare_memory_region((void *) ((char *)k_section_end_virt + 1), upper);
	} else if (mmu_region_contains_single(lower, upper, k_section_start_phys)) {
		if ((void*)((char*)lower + 1) < k_section_start_phys)
			declare_memory_region(lower, (void *) ((char *)k_section_start_phys - 1));
	} else if (mmu_region_contains_single(lower, upper, k_section_end_phys)) {
		if (k_section_end_phys < (void*)((char*)upper - 1))
			declare_memory_region((void *) ((char *)k_section_end_phys + 1), upper);
	} else if (mmu_region_contains_single(lower, upper, k_section_start_virt)) {
		if ((void*)((char*)lower + 1) < k_section_start_virt)
			declare_memory_region(lower, (void *) ((char *)k_section_start_virt - 1));
	} else if (mmu_region_contains_single(lower, upper, k_section_end_virt)) {
		if (k_section_end_virt < (void*)((char*)upper - 1))
			declare_memory_region((void *) ((char *)k_section_end_virt + 1), upper);
	} else {
		mm_add_free_region(lower, upper);
	}
}