[v2 PATCH 1/2] powerpc/pagetable: Add option to dump the linux pagetables
Rashmica Gupta
rashmicy at gmail.com
Tue Mar 29 13:37:00 AEDT 2016
Useful to be able to dump the kernels page tables to check permissions
and memory types - derived from arm64's implementation.
Add a debugfs file to check the page tables. To use this the PPC_PTDUMP
config option must be selected.
Signed-off-by: Rashmica Gupta <rashmicy at gmail.com>
---
Do not check for COMBO pages if default page size is 4K.
arch/powerpc/Kconfig.debug | 12 +
arch/powerpc/mm/Makefile | 1 +
arch/powerpc/mm/dump_linuxpagetables.c | 398 +++++++++++++++++++++++++++++++++
3 files changed, 411 insertions(+)
create mode 100644 arch/powerpc/mm/dump_linuxpagetables.c
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 638f9ce740f5..26a60effea1a 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -344,4 +344,16 @@ config FAIL_IOMMU
If you are unsure, say N.
+config PPC_PTDUMP
+ bool "Export kernel pagetable layout to userspace via debugfs"
+ depends on DEBUG_KERNEL
+ select DEBUG_FS
+ help
+ This option exports the state of the kernel pagetables to a
+ debugfs file. This is only useful for kernel developers who are
+ working in architecture specific areas of the kernel - probably
+ not a good idea to enable this feature in a production kernel.
+
+ If you are unsure, say N.
+
endmenu
diff --git a/arch/powerpc/mm/Makefile b/arch/powerpc/mm/Makefile
index adfee3f1aeb9..6935c6204fbc 100644
--- a/arch/powerpc/mm/Makefile
+++ b/arch/powerpc/mm/Makefile
@@ -41,3 +41,4 @@ obj-$(CONFIG_NOT_COHERENT_CACHE) += dma-noncoherent.o
obj-$(CONFIG_HIGHMEM) += highmem.o
obj-$(CONFIG_PPC_COPRO_BASE) += copro_fault.o
obj-$(CONFIG_SPAPR_TCE_IOMMU) += mmu_context_iommu.o
+obj-$(CONFIG_PPC_PTDUMP) += dump_linuxpagetables.o
diff --git a/arch/powerpc/mm/dump_linuxpagetables.c b/arch/powerpc/mm/dump_linuxpagetables.c
new file mode 100644
index 000000000000..566ae4487a19
--- /dev/null
+++ b/arch/powerpc/mm/dump_linuxpagetables.c
@@ -0,0 +1,398 @@
+/*
+ * Copyright 2016, Rashmica Gupta, IBM Corp.
+ *
+ * This traverses the kernel pagetables and dumps the
+ * information about the used sections of memory to
+ * /sys/kernel/debug/kernel_pagetables.
+ *
+ * Derived from the arm64 implementation:
+ * Copyright (c) 2014, The Linux Foundation, Laura Abbott.
+ * (C) Copyright 2008 Intel Corporation, 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 <linux/debugfs.h>
+#include <linux/fs.h>
+#include <linux/io.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+#include <asm/fixmap.h>
+#include <asm/pgtable.h>
+#include <linux/const.h>
+#include <asm/page.h>
+#include <asm/pgalloc.h>
+
+struct addr_marker {
+ unsigned long start_address;
+ const char *name;
+};
+
+static struct addr_marker address_markers[] = {
+ { VMALLOC_START, "vmalloc() Area" },
+ { VMALLOC_END, "vmalloc() End" },
+ { ISA_IO_BASE, "isa I/O start" },
+ { ISA_IO_END, "isa I/O end" },
+ { PHB_IO_BASE, "phb I/O start" },
+ { PHB_IO_END, "phb I/O end" },
+ { IOREMAP_BASE, "I/O remap start" },
+ { IOREMAP_END, "I/O remap end" },
+ { -1, NULL },
+};
+
+/*
+ * To visualise what is happening,
+ *
+ * - PTRS_PER_P** = how many entries there are in the corresponding P**
+ * - P**_SHIFT = how many bits of the address we use to index into the
+ * corresponding P**
+ * - P**_SIZE is how much memory we can access through the table - not the
+ * size of the table itself.
+ * P**={PGD, PUD, PMD, PTE}
+ *
+ *
+ * Each entry of the PGD points to a PUD. Each entry of a PUD points to a
+ * PMD. Each entry of a PMD points to a PTE. And every PTE entry points to
+ * a page.
+ *
+ * In the case where there are only 3 levels, the PUD is folded into the
+ * PGD: every PUD has only one entry which points to the PMD.
+ *
+ * The page dumper groups page table entries of the same type into a single
+ * description. It uses pg_state to track the range information while
+ * iterating over the PTE entries. When the continuity is broken it then
+ * dumps out a description of the range - ie PTEs that are virtually contiguous
+ * with the same PTE flags are chunked together. This is to make it clear how
+ * different areas of the kernel virtual memory are used.
+ *
+ */
+struct pg_state {
+ struct seq_file *seq;
+ const struct addr_marker *marker;
+ unsigned long start_address;
+ unsigned level;
+ u64 current_flags;
+};
+
+struct flag_info {
+ u64 mask;
+ u64 val;
+ const char *set;
+ const char *clear;
+ bool is_val;
+ int shift;
+};
+
+static const struct flag_info flag_array[] = {
+ {
+ .mask = _PAGE_USER,
+ .val = _PAGE_USER,
+ .set = "user",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_RW,
+ .val = _PAGE_RW,
+ .set = "rw",
+ .clear = "ro",
+ }, {
+ .mask = _PAGE_EXEC,
+ .val = _PAGE_EXEC,
+ .set = " X ",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_PTE,
+ .val = _PAGE_PTE,
+ .set = "pte",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_PRESENT,
+ .val = _PAGE_PRESENT,
+ .set = "present",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_HASHPTE,
+ .val = _PAGE_HASHPTE,
+ .set = "hpte",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_GUARDED,
+ .val = _PAGE_GUARDED,
+ .set = "guarded",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_DIRTY,
+ .val = _PAGE_DIRTY,
+ .set = "dirty",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_ACCESSED,
+ .val = _PAGE_ACCESSED,
+ .set = "accessed",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_WRITETHRU,
+ .val = _PAGE_WRITETHRU,
+ .set = "write through",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_NO_CACHE,
+ .val = _PAGE_NO_CACHE,
+ .set = "no cache",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_BUSY,
+ .val = _PAGE_BUSY,
+ .set = "busy",
+ }, {
+#ifdef CONFIG_PPC_64K_PAGES
+ .mask = _PAGE_COMBO,
+ .val = _PAGE_COMBO,
+ .set = "combo",
+ }, {
+ .mask = _PAGE_4K_PFN,
+ .val = _PAGE_4K_PFN,
+ .set = "4K_pfn",
+ }, {
+#endif
+ .mask = _PAGE_F_GIX,
+ .val = _PAGE_F_GIX,
+ .set = "f_gix",
+ .is_val = true,
+ .shift = _PAGE_F_GIX_SHIFT,
+ }, {
+ .mask = _PAGE_F_SECOND,
+ .val = _PAGE_F_SECOND,
+ .set = "f_second",
+ }, {
+ .mask = _PAGE_SPECIAL,
+ .val = _PAGE_SPECIAL,
+ .set = "special",
+ }
+};
+
+struct pgtable_level {
+ const struct flag_info *flag;
+ size_t num;
+ u64 mask;
+};
+
+static struct pgtable_level pg_level[] = {
+ {
+ }, { /* pgd */
+ .flag = flag_array,
+ .num = ARRAY_SIZE(flag_array),
+ }, { /* pud */
+ .flag = flag_array,
+ .num = ARRAY_SIZE(flag_array),
+ }, { /* pmd */
+ .flag = flag_array,
+ .num = ARRAY_SIZE(flag_array),
+ }, { /* pte */
+ .flag = flag_array,
+ .num = ARRAY_SIZE(flag_array),
+ },
+};
+
+static void dump_flag(struct pg_state *st, const struct flag_info *flag,
+ size_t num)
+{
+ unsigned i;
+
+ for (i = 0; i < num; i++, flag++) {
+ const char *s;
+ u64 val;
+
+ /* flag not defined so don't check it */
+ if (flag->mask == 0)
+ continue;
+
+ if (flag->is_val) {
+ val = st->current_flags & flag->val;
+ if (flag->shift)
+ val = val >> flag->shift;
+ seq_printf(st->seq, " %s:%llx", flag->set, val);
+ } else {
+ if ((st->current_flags & flag->mask) == flag->val)
+ s = flag->set;
+ else
+ s = flag->clear;
+
+ if (s)
+ seq_printf(st->seq, " %s", s);
+ }
+ st->current_flags &= ~flag->mask;
+ }
+ if (st->current_flags != 0)
+ seq_printf(st->seq, " unknown flags:%llx", st->current_flags);
+}
+
+static void dump_addr(struct pg_state *st, unsigned long addr)
+{
+ static const char units[] = "KMGTPE";
+ const char *unit = units;
+ unsigned long delta;
+
+ seq_printf(st->seq, "0x%016lx-0x%016lx ", st->start_address, addr-1);
+ delta = (addr - st->start_address) >> 10;
+ /* Work out what appropriate unit to use */
+ while (!(delta & 1023) && unit[1]) {
+ delta >>= 10;
+ unit++;
+ }
+ seq_printf(st->seq, "%9lu%c", delta, *unit);
+
+}
+
+static void note_page(struct pg_state *st, unsigned long addr, unsigned level,
+ u64 val)
+{
+ u64 flag = val & pg_level[level].mask;
+
+ /* At first no level is set */
+ if (!st->level) {
+ st->level = level;
+ st->current_flags = flag;
+ st->start_address = addr;
+ seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+ /*
+ * Dump the section of virtual memory when:
+ * - the PTE flags from one entry to the next differs.
+ * - we change levels in the tree.
+ * - the address is in a different section of memory and is thus
+ * used for a different purpose, regardless of the flags.
+ */
+ } else if (flag != st->current_flags || level != st->level ||
+ addr >= st->marker[1].start_address) {
+
+ /* Check the PTE flags */
+ if (st->current_flags) {
+ dump_addr(st, addr);
+
+ /* Dump all the flags */
+ if (pg_level[st->level].flag)
+ dump_flag(st, pg_level[st->level].flag,
+ pg_level[st->level].num);
+ seq_puts(st->seq, "\n");
+ }
+
+ /* Address indicates we have passed the end of the
+ * current section of virtual memory
+ */
+ while (addr >= st->marker[1].start_address) {
+ st->marker++;
+ seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+ }
+ st->start_address = addr;
+ st->current_flags = flag;
+ st->level = level;
+ }
+}
+
+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 exists */
+ walk_pte(st, pmd, addr);
+ else
+ note_page(st, addr, 3, pmd_val(*pmd));
+ }
+}
+
+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 exists */
+ walk_pmd(st, pud, addr);
+ else
+ note_page(st, addr, 2, pud_val(*pud));
+ }
+}
+
+static void walk_pgd(struct pg_state *st, unsigned long start)
+{
+ pgd_t *pgd = pgd_offset_k(0UL);
+ unsigned i;
+ unsigned long addr;
+
+ for (i = 0; i < PTRS_PER_PGD; i++, pgd++) {
+ addr = start + i * PGDIR_SIZE;
+ if (!pgd_none(*pgd))
+ /* pgd exists */
+ walk_pud(st, pgd, addr);
+ else
+ note_page(st, addr, 1, pgd_val(*pgd));
+ }
+}
+
+static int ptdump_show(struct seq_file *m, void *v)
+{
+ struct pg_state st = {
+ .seq = m,
+ .start_address = KERN_VIRT_START,
+ .marker = address_markers,
+ };
+ /* Traverse kernel page tables */
+ walk_pgd(&st, KERN_VIRT_START);
+ 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 void build_pgtable_complete_mask(void)
+{
+ unsigned i, j;
+
+ for (i = 0; i < ARRAY_SIZE(pg_level); i++)
+ if (pg_level[i].flag)
+ for (j = 0; j < pg_level[i].num; j++)
+ pg_level[i].mask |= pg_level[i].flag[j].mask;
+}
+
+static int ptdump_init(void)
+{
+ struct dentry *debugfs_file;
+
+ build_pgtable_complete_mask();
+ debugfs_file = debugfs_create_file("kernel_pagetables", 0400, NULL,
+ NULL, &ptdump_fops);
+ return debugfs_file ? 0 : -ENOMEM;
+}
+device_initcall(ptdump_init);
--
2.5.0
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