Re: [PATCH 1/2] powerpc/pagetable: Add option to dump the linux pagetables
From: Balbir Singh <bsingharora@gmail.com>
Date: 2016-03-30 03:24:32
On 22/03/16 09:04, Rashmica Gupta wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- arch/powerpc/Kconfig.debug | 12 ++ arch/powerpc/mm/Makefile | 1 + arch/powerpc/mm/dump_linuxpagetables.c | 377 +++++++++++++++++++++++++++++++++ 3 files changed, 390 insertions(+) create mode 100644 arch/powerpc/mm/dump_linuxpagetables.cdiff --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. +
Some minor comments below, but otherwise Acked-by: Balbir Singh <bsingharora@gmail.com>
quoted hunk ↗ jump to hunk
endmenudiff --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.odiff --git a/arch/powerpc/mm/dump_linuxpagetables.c b/arch/powerpc/mm/dump_linuxpagetables.c new file mode 100644 index 000000000000..f97fbfdac4b9 --- /dev/null +++ b/arch/powerpc/mm/dump_linuxpagetables.c@@ -0,0 +1,377 @@ +/* + * 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; +}; + +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 ",
Can we make this small "x" to sort of go in line with "rw"/"ro"
+ .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",
+ }, {
+ .mask = _PAGE_COMBO,
+ .val = _PAGE_COMBO,
+ .set = "combo",
+ }, {
+ .mask = _PAGE_F_GIX,
+ .val = _PAGE_F_GIX,
+ .set = "f_gix",Can we use "primary"?
+ }, {
+ .mask = _PAGE_F_SECOND,
+ .val = _PAGE_F_SECOND,
+ .set = "f_second","secondary idx"
+ }, {
+ .mask = _PAGE_SPECIAL,
+ .val = _PAGE_SPECIAL,
+ .set = "special",
+ }, {
+ .mask = _PAGE_4K_PFN,
+ .val = _PAGE_4K_PFN,
+ .set = "4K_pfn"
+ }
+};
+
+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;
+
+ if ((st->current_flags & flag->mask) == flag->val)
+ s = flag->set;
+ else
+ s = flag->clear;
+
+ if (s)
+ seq_printf(st->seq, " %s", s);
+ }
+}
+
+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]) {1023, I think ((1 << 10) - 1) is easier to understand but again you may find a better way of encapsulating this
+ 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);