dump_pagetables.c

/*
 * Debug helper to dump the current kernel pagetables of the system
 * so that we can see what the various memory ranges are set to.
 *
 * (C) Copyright 2008 Intel Corporation
 *
 * Author: Arjan van de Ven <arjan@linux.intel.com>
 *
 * 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; version 2
 * of the License.
 */

#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/debugfs.h>

#include <asm/pgtable.h>

/*
 * The dumper groups pagetable entries of the same type into one, and for
 * that it needs to keep some state when walking, and flush this state
 * when a "break" in the continuity is found.
 */
struct pg_state {
	int level;
	pgprot_t current_prot;
	unsigned long start_address;
	unsigned long current_address;
	int printed_vmalloc;
	int printed_modules;
	int printed_vmemmap;
	int printed_highmap;
};

/* Multipliers for offsets within the PTEs */
#define LEVEL_4_MULT (PAGE_SIZE)
#define LEVEL_3_MULT (512UL * LEVEL_4_MULT)
#define LEVEL_2_MULT (512UL * LEVEL_3_MULT)
#define LEVEL_1_MULT (512UL * LEVEL_2_MULT)


/*
 * Print a readable form of a pgprot_t to the seq_file
 */
static void printk_prot(struct seq_file *m, pgprot_t prot, int level)
{
	unsigned long pr = pgprot_val(prot);

	if (pr & _PAGE_USER)
		seq_printf(m, "USR ");
	else
		seq_printf(m, "    ");
	if (pr & _PAGE_RW)
		seq_printf(m, "RW ");
	else
		seq_printf(m, "ro ");
	if (pr & _PAGE_PWT)
		seq_printf(m, "PWT ");
	else
		seq_printf(m, "    ");
	if (pr & _PAGE_PCD)
		seq_printf(m, "PCD ");
	else
		seq_printf(m, "    ");

	/* Bit 9 has a different meaning on level 3 vs 4 */
	if (level <= 3) {
		if (pr & _PAGE_PSE)
			seq_printf(m, "PSE ");
		else
			seq_printf(m, "    ");
	} else {
		if (pr & _PAGE_PAT)
			seq_printf(m, "pat ");
		else
			seq_printf(m, "    ");
	}
	if (pr & _PAGE_GLOBAL)
		seq_printf(m, "GLB ");
	else
		seq_printf(m, "    ");
	if (pr & _PAGE_NX)
		seq_printf(m, "NX ");
	else
		seq_printf(m, "x  ");
}

/*
 * Sign-extend the 48 bit address to 64 bit
 */
static unsigned long sign_extend(unsigned long u)
{
	if (u>>47)
		u = u | (0xffffUL << 48);
	return u;
}

/*
 * This function gets called on a break in a continuous series
 * of PTE entries; the next one is different so we need to
 * print what we collected so far.
 */
static void note_page(struct seq_file *m, struct pg_state *st,
					pgprot_t new_prot, int level)
{
	unsigned long prot, cur;

	/*
	 * If we have a "break" in the series, we need to flush the state that
	 * we have now. "break" is either changing perms or a different level.
	 */
	prot = pgprot_val(new_prot) & ~(PTE_MASK);
	cur = pgprot_val(st->current_prot) & ~(PTE_MASK);

	if ((prot != cur || level != st->level) &&
				st->current_address != st->start_address) {
		char unit = 'K';
		unsigned long delta;

		/*
		 * We print markers for special areas of address space,
		 * such as the start of vmalloc space etc.
		 * This helps in the interpretation.
		 */
		if (!st->printed_vmalloc &&
				st->start_address >= VMALLOC_START) {
			seq_printf(m, "---[ VMALLOC SPACE ]---\n");
			st->printed_vmalloc = 1;
		}
		if (!st->printed_modules &&
				st->start_address >= MODULES_VADDR) {
			seq_printf(m, "---[ MODULES SPACE ]---\n");
			st->printed_modules = 1;
		}
		if (st->printed_modules < 2 &&
				st->start_address >= MODULES_END) {
			seq_printf(m, "---[ END MODULES SPACE ]---\n");
			st->printed_modules = 2;
		}
		if (!st->printed_vmemmap &&
				st->start_address >= VMEMMAP_START) {
			seq_printf(m, "---[ VMMEMMAP SPACE ]---\n");
			st->printed_vmemmap = 1;
		}
		if (!st->printed_highmap &&
				st->start_address >= __START_KERNEL_map) {
			seq_printf(m, "---[ HIGH KERNEL MAPPING ]---\n");
			st->printed_highmap = 1;
		}

		/*
		 * Now print the actual finished series
		 */
		seq_printf(m, "[ %016lx -  %016lx   ",
				st->start_address, st->current_address);

		delta = (st->current_address - st->start_address) >> 10;
		if ((delta & 1023) == 0) {
			delta = delta >> 10;
			unit = 'M';
		}
		if (pgprot_val(st->current_prot)) {
			seq_printf(m, "Size %9lu%cb ", delta, unit);
			printk_prot(m, st->current_prot, st->level);
			seq_printf(m, "L%i]\n", st->level);
		} else {
			/* don't print protections on non-present memory */
			seq_printf(m, "%14lu%cb", delta, unit);
			seq_printf(m, "                           L%i]\n",
					st->level);
		}
		st->start_address = st->current_address;
		st->current_prot = new_prot;
		st->level = level;
	};
}

static void walk_level_4(struct seq_file *m, struct pg_state *st, pmd_t addr,
							unsigned long P)
{
	int i;
	pte_t *start;

	start = (pte_t *) pmd_page_vaddr(addr);
	for (i = 0; i < PTRS_PER_PTE; i++) {
		pgprot_t prot = pte_pgprot(*start);

		st->current_address = sign_extend(P + i * LEVEL_4_MULT);
		note_page(m, st, prot, 4);
		start++;
	}
}


static void walk_level_3(struct seq_file *m, struct pg_state *st, pud_t addr,
							unsigned long P)
{
	int i;
	pmd_t *start;

	start = (pmd_t *) pud_page_vaddr(addr);
	for (i = 0; i < PTRS_PER_PMD; i++) {
		st->current_address = sign_extend(P + i * LEVEL_3_MULT);
		if (!pmd_none(*start)) {
			unsigned long prot;

			prot = pmd_val(*start) & ~(PTE_MASK);
			/* Deal with 2Mb pages */
			if (pmd_large(*start))
				note_page(m, st, __pgprot(prot), 3);
			else
				walk_level_4(m, st, *start,
							P + i * LEVEL_3_MULT);
		} else
			note_page(m, st, __pgprot(0), 3);
		start++;
	}
}


static void walk_level_2(struct seq_file *m, struct pg_state *st, pgd_t addr,
							unsigned long P)
{
	int i;
	pud_t *start;

	start = (pud_t *) pgd_page_vaddr(addr);

	for (i = 0; i < PTRS_PER_PUD; i++) {
		if (!pud_none(*start)) {
			unsigned long prot;

			prot = pud_val(*start) & ~(PTE_MASK);
			/* Deal with 1Gb pages */
			if (pud_large(*start))
				note_page(m, st, __pgprot(prot), 2);
			else
				walk_level_3(m, st, *start,
					P + i * LEVEL_2_MULT);
		} else
			note_page(m, st, __pgprot(0), 2);

		start++;
	}
}

static void walk_level_1(struct seq_file *m)
{
	pgd_t *start = (pgd_t *) &init_level4_pgt;
	int i;
	struct pg_state st;

	memset(&st, 0, sizeof(st));
	st.level = 1;

	for (i = 0; i < PTRS_PER_PGD; i++) {
		if (!pgd_none(*start))
			walk_level_2(m, &st, *start, i * LEVEL_1_MULT);
		else
			note_page(m, &st, __pgprot(0), 1);
		start++;
	}
}

static int ptdump_show(struct seq_file *m, void *v)
{
	seq_puts(m, "Kernel pagetable dump\n");
	walk_level_1(m);
	return 0;
}

static int ptdump_open(struct inode *inode, struct file *filp)
{
	return single_open(filp, ptdump_show, NULL);
}

static const struct file_operations ptdump_fops = {
	.open		= ptdump_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= single_release,
};

int pt_dump_init(void)
{
	struct dentry *pe;

	pe = debugfs_create_file("kernel_page_tables", 0600, NULL, NULL,
				 &ptdump_fops);
	if (!pe)
		return -ENOMEM;

	return 0;
}

__initcall(pt_dump_init);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
MODULE_DESCRIPTION("Kernel debugging helper that dumps pagetables");