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s390/mm: add page table dumper
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This is more or less the same as the x86 page table dumper which was
merged four years ago: 926e539 "x86: add code to dump the (kernel)
page tables for visual inspection by kernel developers".

We add a file at /sys/kernel/debug/kernel_page_tables for debugging
purposes so it's quite easy to see the kernel page table layout and
possible odd mappings:

---[ Identity Mapping ]---
0x0000000000000000-0x0000000000100000        1M PTE RW
---[ Kernel Image Start ]---
0x0000000000100000-0x0000000000800000        7M PMD RO
0x0000000000800000-0x00000000008a9000      676K PTE RO
0x00000000008a9000-0x0000000000900000      348K PTE RW
0x0000000000900000-0x0000000001500000       12M PMD RW
---[ Kernel Image End ]---
0x0000000001500000-0x0000000280000000    10219M PMD RW
0x0000000280000000-0x000003d280000000     3904G PUD I
---[ vmemmap Area ]---
0x000003d280000000-0x000003d288c00000      140M PTE RW
0x000003d288c00000-0x000003d300000000     1908M PMD I
0x000003d300000000-0x000003e000000000       52G PUD I
---[ vmalloc Area ]---
0x000003e000000000-0x000003e000009000       36K PTE RW
0x000003e000009000-0x000003e0000ee000      916K PTE I
0x000003e0000ee000-0x000003e000146000      352K PTE RW
0x000003e000146000-0x000003e000200000      744K PTE I
0x000003e000200000-0x000003e080000000     2046M PMD I
0x000003e080000000-0x0000040000000000      126G PUD I

This usually makes only sense for kernel developers. The output
with CONFIG_DEBUG_PAGEALLOC is not very helpful, because of the
huge number of mapped out pages, however I decided for the time
being to not add a !DEBUG_PAGEALLOC dependency.
Maybe it's helpful for somebody even with that option.

Signed-off-by: Heiko Carstens <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>
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heicarst authored and Martin Schwidefsky committed Oct 9, 2012
1 parent 51eee03 commit e76e82d
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12 changes: 12 additions & 0 deletions arch/s390/Kconfig.debug
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,18 @@ config DEBUG_STRICT_USER_COPY_CHECKS

If unsure, or if you run an older (pre 4.4) gcc, say N.

config S390_PTDUMP
bool "Export kernel pagetable layout to userspace via debugfs"
depends on DEBUG_KERNEL
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_SET_MODULE_RONX
def_bool y
depends on MODULES
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1 change: 1 addition & 0 deletions arch/s390/mm/Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -7,3 +7,4 @@ obj-y := init.o fault.o extmem.o mmap.o vmem.o pgtable.o maccess.o \
obj-$(CONFIG_CMM) += cmm.o
obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
obj-$(CONFIG_DEBUG_SET_MODULE_RONX) += pageattr.o
obj-$(CONFIG_S390_PTDUMP) += dump_pagetables.o
219 changes: 219 additions & 0 deletions arch/s390/mm/dump_pagetables.c
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@@ -0,0 +1,219 @@
#include <linux/seq_file.h>
#include <linux/debugfs.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <asm/sections.h>
#include <asm/pgtable.h>

static unsigned long max_addr;

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

enum address_markers_idx {
IDENTITY_NR = 0,
KERNEL_START_NR,
KERNEL_END_NR,
VMEMMAP_NR,
VMALLOC_NR,
};

static struct addr_marker address_markers[] = {
[IDENTITY_NR] = {0, "Identity Mapping"},
[KERNEL_START_NR] = {(unsigned long)&_stext, "Kernel Image Start"},
[KERNEL_END_NR] = {(unsigned long)&_end, "Kernel Image End"},
[VMEMMAP_NR] = {0, "vmemmap Area"},
[VMALLOC_NR] = {0, "vmalloc Area"},
{ -1, NULL }
};

struct pg_state {
int level;
unsigned int current_prot;
unsigned long start_address;
unsigned long current_address;
const struct addr_marker *marker;
};

static void print_prot(struct seq_file *m, unsigned int pr, int level)
{
static const char * const level_name[] =
{ "ASCE", "PGD", "PUD", "PMD", "PTE" };

seq_printf(m, "%s ", level_name[level]);
if (pr & _PAGE_INVALID)
seq_printf(m, "I\n");
else
seq_printf(m, "%s\n", pr & _PAGE_RO ? "RO" : "RW");
}

static void note_page(struct seq_file *m, struct pg_state *st,
unsigned int new_prot, int level)
{
static const char units[] = "KMGTPE";
int width = sizeof(unsigned long) * 2;
const char *unit = units;
unsigned int prot, cur;
unsigned long delta;

/*
* 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 = new_prot;
cur = st->current_prot;

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) {
/* 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 & 0x3ff) && unit[1]) {
delta >>= 10;
unit++;
}
seq_printf(m, "%9lu%c ", delta, *unit);
print_prot(m, st->current_prot, st->level);
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;
}
}

/*
* The actual page table walker functions. In order to keep the implementation
* of print_prot() short, we only check and pass _PAGE_INVALID and _PAGE_RO
* flags to note_page() if a region, segment or page table entry is invalid or
* read-only.
* After all it's just a hint that the current level being walked contains an
* invalid or read-only entry.
*/
static void walk_pte_level(struct seq_file *m, struct pg_state *st,
pmd_t *pmd, unsigned long addr)
{
unsigned int prot;
pte_t *pte;
int i;

for (i = 0; i < PTRS_PER_PTE && addr < max_addr; i++) {
st->current_address = addr;
pte = pte_offset_kernel(pmd, addr);
prot = pte_val(*pte) & (_PAGE_RO | _PAGE_INVALID);
note_page(m, st, prot, 4);
addr += PAGE_SIZE;
}
}

static void walk_pmd_level(struct seq_file *m, struct pg_state *st,
pud_t *pud, unsigned long addr)
{
unsigned int prot;
pmd_t *pmd;
int i;

for (i = 0; i < PTRS_PER_PMD && addr < max_addr; i++) {
st->current_address = addr;
pmd = pmd_offset(pud, addr);
if (!pmd_none(*pmd)) {
if (pmd_large(*pmd)) {
prot = pmd_val(*pmd) & _SEGMENT_ENTRY_RO;
note_page(m, st, prot, 3);
} else
walk_pte_level(m, st, pmd, addr);
} else
note_page(m, st, _PAGE_INVALID, 3);
addr += PMD_SIZE;
}
}

static void walk_pud_level(struct seq_file *m, struct pg_state *st,
pgd_t *pgd, unsigned long addr)
{
pud_t *pud;
int i;

for (i = 0; i < PTRS_PER_PUD && addr < max_addr; i++) {
st->current_address = addr;
pud = pud_offset(pgd, addr);
if (!pud_none(*pud))
walk_pmd_level(m, st, pud, addr);
else
note_page(m, st, _PAGE_INVALID, 2);
addr += PUD_SIZE;
}
}

static void walk_pgd_level(struct seq_file *m)
{
unsigned long addr = 0;
struct pg_state st;
pgd_t *pgd;
int i;

memset(&st, 0, sizeof(st));
for (i = 0; i < PTRS_PER_PGD && addr < max_addr; i++) {
st.current_address = addr;
pgd = pgd_offset_k(addr);
if (!pgd_none(*pgd))
walk_pud_level(m, &st, pgd, addr);
else
note_page(m, &st, _PAGE_INVALID, 1);
addr += PGDIR_SIZE;
}
/* Flush out the last page */
st.current_address = max_addr;
note_page(m, &st, 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)
{
/*
* Figure out the maximum virtual address being accessible with the
* kernel ASCE. We need this to keep the page table walker functions
* from accessing non-existent entries.
*/
#ifdef CONFIG_64BIT
max_addr = (S390_lowcore.kernel_asce & _REGION_ENTRY_TYPE_MASK) >> 2;
max_addr = 1UL << (max_addr * 11 + 31);
#else
max_addr = 1UL << 31;
#endif
address_markers[VMEMMAP_NR].start_address = (unsigned long) vmemmap;
address_markers[VMALLOC_NR].start_address = VMALLOC_START;
debugfs_create_file("kernel_page_tables", 0400, NULL, NULL, &ptdump_fops);
return 0;
}
device_initcall(pt_dump_init);

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