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Commit e76e82d7 authored by Heiko Carstens's avatar Heiko Carstens Committed by Martin Schwidefsky
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s390/mm: add page table dumper 



This is more or less the same as the x86 page table dumper which was
merged four years ago: 926e5392 "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: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 51eee033

arch/s390/Kconfig.debug

+12 −0
Original line number Diff line number Diff line
@@ -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

arch/s390/mm/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/s390/mm/dump_pagetables.c

0 → 100644
+219 −0
Original line number Diff line number Diff line 
#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);