arm64: add support to dump the kernel page tables

In a similar manner to arm, it's useful to be able to dump the page
tables to verify permissions and memory types. Add a debugfs file
to check the page tables.
Acked-by: Steve Capper <steve.capper@linaro.org>
Tested-by: Steve Capper <steve.capper@linaro.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
[will: s/BUFFERABLE/NORMAL-NC/]
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/Kconfig.debug

@@ -6,6 +6,18 @@ config FRAME_POINTER
 	bool
 	default y
 
+config ARM64_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 STRICT_DEVMEM
 	bool "Filter access to /dev/mem"
 	depends on MMU

arch/arm64/mm/Makefile

@@ -3,3 +3,4 @@ obj-y				:= dma-mapping.o extable.o fault.o init.o \
 				   ioremap.o mmap.o pgd.o mmu.o \
 				   context.o proc.o pageattr.o
 obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
+obj-$(CONFIG_ARM64_PTDUMP)	+= dump.o

arch/arm64/mm/dump.c

+/*
+ * Copyright (c) 2014, The Linux Foundation. All rights reserved.
+ * Debug helper to dump the current kernel pagetables of the system
+ * so that we can see what the various memory ranges are set to.
+ *
+ * Derived from x86 and arm implementation:
+ * (C) Copyright 2008 Intel Corporation
+ *
+ * Author: Arjan van de Ven <arjan@linux.intel.com>
+ *
+ * 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/fs.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+
+#include <asm/fixmap.h>
+#include <asm/pgtable.h>
+
+#define LOWEST_ADDR	(UL(0xffffffffffffffff) << VA_BITS)
+
+struct addr_marker {
+	unsigned long start_address;
+	const char *name;
+};
+
+enum address_markers_idx {
+	VMALLOC_START_NR = 0,
+	VMALLOC_END_NR,
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+	VMEMMAP_START_NR,
+	VMEMMAP_END_NR,
+#endif
+	PCI_START_NR,
+	PCI_END_NR,
+	FIXADDR_START_NR,
+	FIXADDR_END_NR,
+	MODULES_START_NR,
+	MODUELS_END_NR,
+	KERNEL_SPACE_NR,
+};
+
+static struct addr_marker address_markers[] = {
+	{ VMALLOC_START,	"vmalloc() Area" },
+	{ VMALLOC_END,		"vmalloc() End" },
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+	{ 0,			"vmemmap start" },
+	{ 0,			"vmemmap end" },
+#endif
+	{ (unsigned long) PCI_IOBASE,		"PCI I/O start" },
+	{ (unsigned long) PCI_IOBASE + SZ_16M,	"PCI I/O end" },
+	{ FIXADDR_START,	"Fixmap start" },
+	{ FIXADDR_TOP,		"Fixmap end" },
+	{ MODULES_VADDR,	"Modules start" },
+	{ MODULES_END,		"Modules end" },
+	{ PAGE_OFFSET,		"Kernel Mapping" },
+	{ -1,			NULL },
+};
+
+struct pg_state {
+	struct seq_file *seq;
+	const struct addr_marker *marker;
+	unsigned long start_address;
+	unsigned level;
+	u64 current_prot;
+};
+
+struct prot_bits {
+	u64		mask;
+	u64		val;
+	const char	*set;
+	const char	*clear;
+};
+
+static const struct prot_bits pte_bits[] = {
+	{
+		.mask	= PTE_USER,
+		.val	= PTE_USER,
+		.set	= "USR",
+		.clear	= "   ",
+	}, {
+		.mask	= PTE_RDONLY,
+		.val	= PTE_RDONLY,
+		.set	= "ro",
+		.clear	= "RW",
+	}, {
+		.mask	= PTE_PXN,
+		.val	= PTE_PXN,
+		.set	= "NX",
+		.clear	= "x ",
+	}, {
+		.mask	= PTE_SHARED,
+		.val	= PTE_SHARED,
+		.set	= "SHD",
+		.clear	= "   ",
+	}, {
+		.mask	= PTE_AF,
+		.val	= PTE_AF,
+		.set	= "AF",
+		.clear	= "  ",
+	}, {
+		.mask	= PTE_NG,
+		.val	= PTE_NG,
+		.set	= "NG",
+		.clear	= "  ",
+	}, {
+		.mask	= PTE_UXN,
+		.val	= PTE_UXN,
+		.set	= "UXN",
+	}, {
+		.mask	= PTE_ATTRINDX_MASK,
+		.val	= PTE_ATTRINDX(MT_DEVICE_nGnRnE),
+		.set	= "DEVICE/nGnRnE",
+	}, {
+		.mask	= PTE_ATTRINDX_MASK,
+		.val	= PTE_ATTRINDX(MT_DEVICE_nGnRE),
+		.set	= "DEVICE/nGnRE",
+	}, {
+		.mask	= PTE_ATTRINDX_MASK,
+		.val	= PTE_ATTRINDX(MT_DEVICE_GRE),
+		.set	= "DEVICE/GRE",
+	}, {
+		.mask	= PTE_ATTRINDX_MASK,
+		.val	= PTE_ATTRINDX(MT_NORMAL_NC),
+		.set	= "MEM/NORMAL-NC",
+	}, {
+		.mask	= PTE_ATTRINDX_MASK,
+		.val	= PTE_ATTRINDX(MT_NORMAL),
+		.set	= "MEM/NORMAL",
+	}
+};
+
+struct pg_level {
+	const struct prot_bits *bits;
+	size_t num;
+	u64 mask;
+};
+
+static struct pg_level pg_level[] = {
+	{
+	}, { /* pgd */
+		.bits	= pte_bits,
+		.num	= ARRAY_SIZE(pte_bits),
+	}, { /* pud */
+		.bits	= pte_bits,
+		.num	= ARRAY_SIZE(pte_bits),
+	}, { /* pmd */
+		.bits	= pte_bits,
+		.num	= ARRAY_SIZE(pte_bits),
+	}, { /* pte */
+		.bits	= pte_bits,
+		.num	= ARRAY_SIZE(pte_bits),
+	},
+};
+
+static void dump_prot(struct pg_state *st, const struct prot_bits *bits,
+			size_t num)
+{
+	unsigned i;
+
+	for (i = 0; i < num; i++, bits++) {
+		const char *s;
+
+		if ((st->current_prot & bits->mask) == bits->val)
+			s = bits->set;
+		else
+			s = bits->clear;
+
+		if (s)
+			seq_printf(st->seq, " %s", s);
+	}
+}
+
+static void note_page(struct pg_state *st, unsigned long addr, unsigned level,
+				u64 val)
+{
+	static const char units[] = "KMGTPE";
+	u64 prot = val & pg_level[level].mask;
+
+	if (addr < LOWEST_ADDR)
+		return;
+
+	if (!st->level) {
+		st->level = level;
+		st->current_prot = prot;
+		st->start_address = addr;
+		seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+	} else if (prot != st->current_prot || level != st->level ||
+		   addr >= st->marker[1].start_address) {
+		const char *unit = units;
+		unsigned long delta;
+
+		if (st->current_prot) {
+			seq_printf(st->seq, "0x%16lx-0x%16lx   ",
+				   st->start_address, addr);
+
+			delta = (addr - st->start_address) >> 10;
+			while (!(delta & 1023) && unit[1]) {
+				delta >>= 10;
+				unit++;
+			}
+			seq_printf(st->seq, "%9lu%c", delta, *unit);
+			if (pg_level[st->level].bits)
+				dump_prot(st, pg_level[st->level].bits,
+					  pg_level[st->level].num);
+			seq_puts(st->seq, "\n");
+		}
+
+		if (addr >= st->marker[1].start_address) {
+			st->marker++;
+			seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+		}
+
+		st->start_address = addr;
+		st->current_prot = prot;
+		st->level = level;
+	}
+
+	if (addr >= st->marker[1].start_address) {
+		st->marker++;
+		seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+	}
+
+}
+
+static void walk_pte(struct pg_state *st, pmd_t *pmd, unsigned long start)
+{
+	pte_t *pte = pte_offset_kernel(pmd, 0);
+	unsigned long addr;
+	unsigned i;
+
+	for (i = 0; i < PTRS_PER_PTE; i++, pte++) {
+		addr = start + i * PAGE_SIZE;
+		note_page(st, addr, 4, pte_val(*pte));
+	}
+}
+
+static void walk_pmd(struct pg_state *st, pud_t *pud, unsigned long start)
+{
+	pmd_t *pmd = pmd_offset(pud, 0);
+	unsigned long addr;
+	unsigned i;
+
+	for (i = 0; i < PTRS_PER_PMD; i++, pmd++) {
+		addr = start + i * PMD_SIZE;
+		if (pmd_none(*pmd) || pmd_sect(*pmd) || pmd_bad(*pmd))
+			note_page(st, addr, 3, pmd_val(*pmd));
+		else
+			walk_pte(st, pmd, addr);
+	}
+}
+
+static void walk_pud(struct pg_state *st, pgd_t *pgd, unsigned long start)
+{
+	pud_t *pud = pud_offset(pgd, 0);
+	unsigned long addr;
+	unsigned i;
+
+	for (i = 0; i < PTRS_PER_PUD; i++, pud++) {
+		addr = start + i * PUD_SIZE;
+		if (pud_none(*pud) || pud_sect(*pud) || pud_bad(*pud))
+			note_page(st, addr, 2, pud_val(*pud));
+		else
+			walk_pmd(st, pud, addr);
+	}
+}
+
+static void walk_pgd(struct pg_state *st, struct mm_struct *mm, unsigned long start)
+{
+	pgd_t *pgd = pgd_offset(mm, 0);
+	unsigned i;
+	unsigned long addr;
+
+	for (i = 0; i < PTRS_PER_PGD; i++, pgd++) {
+		addr = start + i * PGDIR_SIZE;
+		if (pgd_none(*pgd) || pgd_bad(*pgd))
+			note_page(st, addr, 1, pgd_val(*pgd));
+		else
+			walk_pud(st, pgd, addr);
+	}
+}
+
+static int ptdump_show(struct seq_file *m, void *v)
+{
+	struct pg_state st = {
+		.seq = m,
+		.marker = address_markers,
+	};
+
+	walk_pgd(&st, &init_mm, LOWEST_ADDR);
+
+	note_page(&st, 0, 0, 0);
+	return 0;
+}
+
+static int ptdump_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, ptdump_show, NULL);
+}
+
+static const struct file_operations ptdump_fops = {
+	.open		= ptdump_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static int ptdump_init(void)
+{
+	struct dentry *pe;
+	unsigned i, j;
+
+	for (i = 0; i < ARRAY_SIZE(pg_level); i++)
+		if (pg_level[i].bits)
+			for (j = 0; j < pg_level[i].num; j++)
+				pg_level[i].mask |= pg_level[i].bits[j].mask;
+
+	address_markers[VMEMMAP_START_NR].start_address =
+				(unsigned long)virt_to_page(PAGE_OFFSET);
+	address_markers[VMEMMAP_END_NR].start_address =
+				(unsigned long)virt_to_page(high_memory);
+
+	pe = debugfs_create_file("kernel_page_tables", 0400, NULL, NULL,
+				 &ptdump_fops);
+	return pe ? 0 : -ENOMEM;
+}
+device_initcall(ptdump_init);