dump_pagetables.c

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/*
 * 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 <[email protected]>
 *
 * 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/debugfs.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/seq_file.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;
    const struct addr_marker *marker;
};

struct addr_marker {
    unsigned long start_address;
    const char *name;
};

/* indices for address_markers; keep sync'd w/ address_markers below */
enum address_markers_idx {
    USER_SPACE_NR = 0,
#ifdef CONFIG_X86_64
    KERNEL_SPACE_NR,
    LOW_KERNEL_NR,
    VMALLOC_START_NR,
    VMEMMAP_START_NR,
    HIGH_KERNEL_NR,
    MODULES_VADDR_NR,
    MODULES_END_NR,
#else
    KERNEL_SPACE_NR,
    VMALLOC_START_NR,
    VMALLOC_END_NR,
# ifdef CONFIG_HIGHMEM
    PKMAP_BASE_NR,
# endif
    FIXADDR_START_NR,
#endif
};

/* Address space markers hints */
static struct addr_marker address_markers[] = {
    { 0, "User Space" },
#ifdef CONFIG_X86_64
    { 0x8000000000000000UL, "Kernel Space" },
    { PAGE_OFFSET,      "Low Kernel Mapping" },
    { VMALLOC_START,        "vmalloc() Area" },
    { VMEMMAP_START,        "Vmemmap" },
    { __START_KERNEL_map,   "High Kernel Mapping" },
    { MODULES_VADDR,        "Modules" },
    { MODULES_END,          "End Modules" },
#else
    { PAGE_OFFSET,          "Kernel Mapping" },
    { 0/* VMALLOC_START */, "vmalloc() Area" },
    { 0/*VMALLOC_END*/,     "vmalloc() End" },
# ifdef CONFIG_HIGHMEM
    { 0/*PKMAP_BASE*/,      "Persisent kmap() Area" },
# endif
    { 0/*FIXADDR_START*/,   "Fixmap Area" },
#endif
    { -1, NULL }        /* End of list */
};

/* Multipliers for offsets within the PTEs */
#define PTE_LEVEL_MULT (PAGE_SIZE)
#define PMD_LEVEL_MULT (PTRS_PER_PTE * PTE_LEVEL_MULT)
#define PUD_LEVEL_MULT (PTRS_PER_PMD * PMD_LEVEL_MULT)
#define PGD_LEVEL_MULT (PTRS_PER_PUD * PUD_LEVEL_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)
{
    pgprotval_t pr = pgprot_val(prot);
    static const char * const level_name[] =
        { "cr3", "pgd", "pud", "pmd", "pte" };

    if (!pgprot_val(prot)) {
        /* Not present */
        seq_printf(m, "                          ");
    } else {
        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  ");
    }
    seq_printf(m, "%s\n", level_name[level]);
}

/*
 * On 64 bits, sign-extend the 48 bit address to 64 bit
 */
static unsigned long normalize_addr(unsigned long u)
{
#ifdef CONFIG_X86_64
    return (signed long)(u << 16) >> 16;
#else
    return u;
#endif
}

/*
 * 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)
{
    pgprotval_t prot, cur;
    static const char units[] = "KMGTPE";

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

    if (!st->level) {
        /* First entry */
        st->current_prot = new_prot;
        st->level = level;
        st->marker = address_markers;
        seq_printf(m, "---[ %s ]---\n", st->marker->name);
    } else if (prot != cur || level != st->level ||
           st->current_address >= st->marker[1].start_address) {
        const char *unit = units;
        unsigned long delta;
        int width = sizeof(unsigned long) * 2;

        /*
         * Now print the actual finished series
         */
        seq_printf(m, "0x%0*lx-0x%0*lx   ",
               width, st->start_address,
               width, st->current_address);

        delta = (st->current_address - st->start_address) >> 10;
        while (!(delta & 1023) && unit[1]) {
            delta >>= 10;
            unit++;
        }
        seq_printf(m, "%9lu%c ", delta, *unit);
        printk_prot(m, st->current_prot, st->level);

        /*
         * We print markers for special areas of address space,
         * such as the start of vmalloc space etc.
         * This helps in the interpretation.
         */
        if (st->current_address >= st->marker[1].start_address) {
            st->marker++;
            seq_printf(m, "---[ %s ]---\n", st->marker->name);
        }

        st->start_address = st->current_address;
        st->current_prot = new_prot;
        st->level = level;
    }
}

static void walk_pte_level(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 = normalize_addr(P + i * PTE_LEVEL_MULT);
        note_page(m, st, prot, 4);
        start++;
    }
}

#if PTRS_PER_PMD > 1

static void walk_pmd_level(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 = normalize_addr(P + i * PMD_LEVEL_MULT);
        if (!pmd_none(*start)) {
            pgprotval_t prot = pmd_val(*start) & PTE_FLAGS_MASK;

            if (pmd_large(*start) || !pmd_present(*start))
                note_page(m, st, __pgprot(prot), 3);
            else
                walk_pte_level(m, st, *start,
                           P + i * PMD_LEVEL_MULT);
        } else
            note_page(m, st, __pgprot(0), 3);
        start++;
    }
}

#else
#define walk_pmd_level(m,s,a,p) walk_pte_level(m,s,__pmd(pud_val(a)),p)
#define pud_large(a) pmd_large(__pmd(pud_val(a)))
#define pud_none(a)  pmd_none(__pmd(pud_val(a)))
#endif

#if PTRS_PER_PUD > 1

static void walk_pud_level(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++) {
        st->current_address = normalize_addr(P + i * PUD_LEVEL_MULT);
        if (!pud_none(*start)) {
            pgprotval_t prot = pud_val(*start) & PTE_FLAGS_MASK;

            if (pud_large(*start) || !pud_present(*start))
                note_page(m, st, __pgprot(prot), 2);
            else
                walk_pmd_level(m, st, *start,
                           P + i * PUD_LEVEL_MULT);
        } else
            note_page(m, st, __pgprot(0), 2);

        start++;
    }
}

#else
#define walk_pud_level(m,s,a,p) walk_pmd_level(m,s,__pud(pgd_val(a)),p)
#define pgd_large(a) pud_large(__pud(pgd_val(a)))
#define pgd_none(a)  pud_none(__pud(pgd_val(a)))
#endif

static void walk_pgd_level(struct seq_file *m)
{
#ifdef CONFIG_X86_64
    pgd_t *start = (pgd_t *) &init_level4_pgt;
#else
    pgd_t *start = swapper_pg_dir;
#endif
    int i;
    struct pg_state st;

    memset(&st, 0, sizeof(st));

    for (i = 0; i < PTRS_PER_PGD; i++) {
        st.current_address = normalize_addr(i * PGD_LEVEL_MULT);
        if (!pgd_none(*start)) {
            pgprotval_t prot = pgd_val(*start) & PTE_FLAGS_MASK;

            if (pgd_large(*start) || !pgd_present(*start))
                note_page(m, &st, __pgprot(prot), 1);
            else
                walk_pud_level(m, &st, *start,
                           i * PGD_LEVEL_MULT);
        } else
            note_page(m, &st, __pgprot(0), 1);

        start++;
    }

    /* Flush out the last page */
    st.current_address = normalize_addr(PTRS_PER_PGD*PGD_LEVEL_MULT);
    note_page(m, &st, __pgprot(0), 0);
}

static int ptdump_show(struct seq_file *m, void *v)
{
    walk_pgd_level(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,
};

static int pt_dump_init(void)
{
    struct dentry *pe;

#ifdef CONFIG_X86_32
    /* Not a compile-time constant on x86-32 */
    address_markers[VMALLOC_START_NR].start_address = VMALLOC_START;
    address_markers[VMALLOC_END_NR].start_address = VMALLOC_END;
# ifdef CONFIG_HIGHMEM
    address_markers[PKMAP_BASE_NR].start_address = PKMAP_BASE;
# endif
    address_markers[FIXADDR_START_NR].start_address = FIXADDR_START;
#endif

    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 <[email protected]>");
MODULE_DESCRIPTION("Kernel debugging helper that dumps pagetables");