From 926e5392ba8a388ae32ca0d2714cc2c73945c609 Mon Sep 17 00:00:00 2001 From: Arjan van de Ven Date: Thu, 17 Apr 2008 17:40:45 +0200 Subject: [PATCH] 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 Cc: mingo@elte.hu Cc: tglx@tglx.de Cc: hpa@zytor.com Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner --- arch/x86/Kconfig.debug | 12 ++ arch/x86/mm/Makefile | 1 + arch/x86/mm/dump_pagetables.c | 301 ++++++++++++++++++++++++++++++++++ 3 files changed, 314 insertions(+) create mode 100644 arch/x86/mm/dump_pagetables.c diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index 702eb39901ca..cb7002eca887 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -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 diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile index 8e81660604bc..28632f42ca66 100644 --- a/arch/x86/mm/Makefile +++ b/arch/x86/mm/Makefile @@ -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 diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c new file mode 100644 index 000000000000..5e7f6430c27e --- /dev/null +++ b/arch/x86/mm/dump_pagetables.c @@ -0,0 +1,301 @@ +/* + * 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 + * + * 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 +#include +#include + +#include + +/* + * 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 "); +MODULE_DESCRIPTION("Kernel debugging helper that dumps pagetables"); -- 2.20.1