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: Arjan van de Ven <arjan@linux.intel.com> Cc: mingo@elte.hu Cc: tglx@tglx.de Cc: hpa@zytor.com Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Arjan van de Ven
Ingo Molnar
parent
2596e0fae0
commit
926e5392ba
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@ -54,6 +54,18 @@ config DEBUG_PER_CPU_MAPS
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Say N if unsure.
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config X86_PTDUMP
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bool "Export kernel pagetable layout to userspace via debugfs"
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depends on X86_64
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select DEBUG_FS
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help
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Say Y here if you want to show the kernel pagetable layout in a
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debugfs file. This information is only useful for kernel developers
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who are working in architecture specific areas of the kernel.
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It is probably not a good idea to enable this feature in a production
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kernel.
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If in doubt, say "N"
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config DEBUG_RODATA
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bool "Write protect kernel read-only data structures"
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default y
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@ -12,4 +12,5 @@ else
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obj-$(CONFIG_NUMA) += numa_64.o
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obj-$(CONFIG_K8_NUMA) += k8topology_64.o
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obj-$(CONFIG_ACPI_NUMA) += srat_64.o
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obj-$(CONFIG_X86_PTDUMP) += dump_pagetables.o
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endif
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@ -0,0 +1,301 @@
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/*
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* Debug helper to dump the current kernel pagetables of the system
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* so that we can see what the various memory ranges are set to.
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*
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* (C) Copyright 2008 Intel Corporation
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*
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* Author: Arjan van de Ven <arjan@linux.intel.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; version 2
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* of the License.
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*/
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#include <linux/module.h>
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#include <linux/seq_file.h>
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#include <linux/debugfs.h>
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#include <asm/pgtable.h>
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/*
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* The dumper groups pagetable entries of the same type into one, and for
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* that it needs to keep some state when walking, and flush this state
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* when a "break" in the continuity is found.
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*/
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struct pg_state {
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int level;
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pgprot_t current_prot;
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unsigned long start_address;
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unsigned long current_address;
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int printed_vmalloc;
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int printed_modules;
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int printed_vmemmap;
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int printed_highmap;
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};
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/* Multipliers for offsets within the PTEs */
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#define LEVEL_4_MULT (PAGE_SIZE)
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#define LEVEL_3_MULT (512UL * LEVEL_4_MULT)
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#define LEVEL_2_MULT (512UL * LEVEL_3_MULT)
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#define LEVEL_1_MULT (512UL * LEVEL_2_MULT)
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/*
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* Print a readable form of a pgprot_t to the seq_file
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*/
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static void printk_prot(struct seq_file *m, pgprot_t prot, int level)
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{
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unsigned long pr = pgprot_val(prot);
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if (pr & _PAGE_USER)
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seq_printf(m, "USR ");
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else
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seq_printf(m, " ");
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if (pr & _PAGE_RW)
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seq_printf(m, "RW ");
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else
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seq_printf(m, "ro ");
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if (pr & _PAGE_PWT)
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seq_printf(m, "PWT ");
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else
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seq_printf(m, " ");
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if (pr & _PAGE_PCD)
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seq_printf(m, "PCD ");
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else
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seq_printf(m, " ");
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/* Bit 9 has a different meaning on level 3 vs 4 */
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if (level <= 3) {
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if (pr & _PAGE_PSE)
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seq_printf(m, "PSE ");
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else
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seq_printf(m, " ");
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} else {
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if (pr & _PAGE_PAT)
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seq_printf(m, "pat ");
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else
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seq_printf(m, " ");
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}
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if (pr & _PAGE_GLOBAL)
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seq_printf(m, "GLB ");
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else
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seq_printf(m, " ");
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if (pr & _PAGE_NX)
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seq_printf(m, "NX ");
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else
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seq_printf(m, "x ");
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}
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/*
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* Sign-extend the 48 bit address to 64 bit
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*/
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static unsigned long sign_extend(unsigned long u)
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{
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if (u>>47)
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u = u | (0xffffUL << 48);
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return u;
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}
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/*
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* This function gets called on a break in a continuous series
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* of PTE entries; the next one is different so we need to
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* print what we collected so far.
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*/
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static void note_page(struct seq_file *m, struct pg_state *st,
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pgprot_t new_prot, int level)
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{
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unsigned long prot, cur;
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/*
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* If we have a "break" in the series, we need to flush the state that
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* we have now. "break" is either changing perms or a different level.
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*/
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prot = pgprot_val(new_prot) & ~(PTE_MASK);
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cur = pgprot_val(st->current_prot) & ~(PTE_MASK);
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if ((prot != cur || level != st->level) &&
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st->current_address != st->start_address) {
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char unit = 'K';
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unsigned long delta;
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/*
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* We print markers for special areas of address space,
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* such as the start of vmalloc space etc.
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* This helps in the interpretation.
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*/
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if (!st->printed_vmalloc &&
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st->start_address >= VMALLOC_START) {
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seq_printf(m, "---[ VMALLOC SPACE ]---\n");
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st->printed_vmalloc = 1;
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}
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if (!st->printed_modules &&
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st->start_address >= MODULES_VADDR) {
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seq_printf(m, "---[ MODULES SPACE ]---\n");
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st->printed_modules = 1;
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}
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if (st->printed_modules < 2 &&
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st->start_address >= MODULES_END) {
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seq_printf(m, "---[ END MODULES SPACE ]---\n");
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st->printed_modules = 2;
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}
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if (!st->printed_vmemmap &&
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st->start_address >= VMEMMAP_START) {
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seq_printf(m, "---[ VMMEMMAP SPACE ]---\n");
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st->printed_vmemmap = 1;
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}
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if (!st->printed_highmap &&
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st->start_address >= __START_KERNEL_map) {
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seq_printf(m, "---[ HIGH KERNEL MAPPING ]---\n");
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st->printed_highmap = 1;
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}
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/*
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* Now print the actual finished series
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*/
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seq_printf(m, "[ %016lx - %016lx ",
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st->start_address, st->current_address);
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delta = (st->current_address - st->start_address) >> 10;
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if ((delta & 1023) == 0) {
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delta = delta >> 10;
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unit = 'M';
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}
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if (pgprot_val(st->current_prot)) {
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seq_printf(m, "Size %9lu%cb ", delta, unit);
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printk_prot(m, st->current_prot, st->level);
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seq_printf(m, "L%i]\n", st->level);
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} else {
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/* don't print protections on non-present memory */
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seq_printf(m, "%14lu%cb", delta, unit);
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seq_printf(m, " L%i]\n",
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st->level);
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}
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st->start_address = st->current_address;
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st->current_prot = new_prot;
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st->level = level;
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};
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}
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static void walk_level_4(struct seq_file *m, struct pg_state *st, pmd_t addr,
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unsigned long P)
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{
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int i;
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pte_t *start;
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start = (pte_t *) pmd_page_vaddr(addr);
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for (i = 0; i < PTRS_PER_PTE; i++) {
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pgprot_t prot = pte_pgprot(*start);
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st->current_address = sign_extend(P + i * LEVEL_4_MULT);
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note_page(m, st, prot, 4);
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start++;
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}
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}
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static void walk_level_3(struct seq_file *m, struct pg_state *st, pud_t addr,
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unsigned long P)
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{
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int i;
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pmd_t *start;
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start = (pmd_t *) pud_page_vaddr(addr);
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for (i = 0; i < PTRS_PER_PMD; i++) {
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st->current_address = sign_extend(P + i * LEVEL_3_MULT);
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if (!pmd_none(*start)) {
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unsigned long prot;
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prot = pmd_val(*start) & ~(PTE_MASK);
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/* Deal with 2Mb pages */
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if (pmd_large(*start))
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note_page(m, st, __pgprot(prot), 3);
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else
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walk_level_4(m, st, *start,
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P + i * LEVEL_3_MULT);
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} else
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note_page(m, st, __pgprot(0), 3);
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start++;
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}
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}
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static void walk_level_2(struct seq_file *m, struct pg_state *st, pgd_t addr,
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unsigned long P)
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{
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int i;
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pud_t *start;
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start = (pud_t *) pgd_page_vaddr(addr);
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for (i = 0; i < PTRS_PER_PUD; i++) {
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if (!pud_none(*start)) {
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unsigned long prot;
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prot = pud_val(*start) & ~(PTE_MASK);
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/* Deal with 1Gb pages */
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if (pud_large(*start))
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note_page(m, st, __pgprot(prot), 2);
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else
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walk_level_3(m, st, *start,
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P + i * LEVEL_2_MULT);
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} else
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note_page(m, st, __pgprot(0), 2);
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start++;
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}
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}
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static void walk_level_1(struct seq_file *m)
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{
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pgd_t *start = (pgd_t *) &init_level4_pgt;
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int i;
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struct pg_state st;
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memset(&st, 0, sizeof(st));
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st.level = 1;
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for (i = 0; i < PTRS_PER_PGD; i++) {
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if (!pgd_none(*start))
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walk_level_2(m, &st, *start, i * LEVEL_1_MULT);
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else
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note_page(m, &st, __pgprot(0), 1);
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start++;
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}
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}
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static int ptdump_show(struct seq_file *m, void *v)
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{
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seq_puts(m, "Kernel pagetable dump\n");
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walk_level_1(m);
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return 0;
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}
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static int ptdump_open(struct inode *inode, struct file *filp)
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{
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return single_open(filp, ptdump_show, NULL);
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}
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static const struct file_operations ptdump_fops = {
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.open = ptdump_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = single_release,
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};
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int pt_dump_init(void)
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{
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struct dentry *pe;
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pe = debugfs_create_file("kernel_page_tables", 0600, NULL, NULL,
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&ptdump_fops);
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if (!pe)
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return -ENOMEM;
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return 0;
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}
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__initcall(pt_dump_init);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
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MODULE_DESCRIPTION("Kernel debugging helper that dumps pagetables");
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