Commit 926e5392 authored by Arjan van de Ven's avatar Arjan van de Ven Committed by Ingo Molnar
Browse files

x86: add code to dump the (kernel) page tables for visual inspection by kernel developers 



This patch adds code to the kernel to have an (optional)
/proc/kernel_page_tables debug file that basically dumps the kernel
pagetables; this allows us kernel developers to verify that nothing fishy is
going on and that the various mappings are set up correctly. This was quite
useful in finding various change_page_attr() bugs, and is very likely to be
useful in the future as well.

Signed-off-by: default avatarArjan van de Ven <arjan@linux.intel.com>
Cc: mingo@elte.hu
Cc: tglx@tglx.de
Cc: hpa@zytor.com
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 2596e0fa

arch/x86/Kconfig.debug

+12 −0
Original line number Diff line number Diff line
@@ -54,6 +54,18 @@ config DEBUG_PER_CPU_MAPS 


	  Say N if unsure.



config X86_PTDUMP

	bool "Export kernel pagetable layout to userspace via debugfs"

	depends on X86_64

	select DEBUG_FS

	help

	  Say Y here if you want to show the kernel pagetable layout in a

	  debugfs file. This information is only useful for kernel developers

	  who are working in architecture specific areas of the kernel.

	  It is probably not a good idea to enable this feature in a production

	  kernel.

	  If in doubt, say "N"



config DEBUG_RODATA

	bool "Write protect kernel read-only data structures"

	default y

arch/x86/mm/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -12,4 +12,5 @@ else 
obj-$(CONFIG_NUMA)		+= numa_64.o

obj-$(CONFIG_K8_NUMA)		+= k8topology_64.o

obj-$(CONFIG_ACPI_NUMA)		+= srat_64.o

obj-$(CONFIG_X86_PTDUMP)	+= dump_pagetables.o

endif

arch/x86/mm/dump_pagetables.c

0 → 100644
+301 −0
Original line number Diff line number Diff line 
/*

 * 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");

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