[patch 064/158] mm: add generic ptdump

akpm
2019-12-01T01:53:08Z

From: Steven Price <steven.price@arm.com>
Subject: mm: add generic ptdump

Add a generic version of page table dumping that architectures can opt-in
to

[steven.price@arm.com: v15]
Link: http://lkml.kernel.org/r/20191101140942.51554-20-steven.price@arm.com
[cai@lca.pw: fix a -Wold-style-declaration warning]
Link: http://lkml.kernel.org/r/1572895385-29194-1-git-send-email-cai@lca.pw
Link: http://lkml.kernel.org/r/20191028135910.33253-20-steven.price@arm.com
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Qian Cai <cai@lca.pw>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Potapenko <glider@google.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: James Hogan <jhogan@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: "Liang, Kan" <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Shiraz Hashim <shashim@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zong Li <zong.li@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/ptdump.h | 21 +++++
mm/Kconfig.debug | 21 +++++
mm/Makefile | 1
mm/ptdump.c | 151 +++++++++++++++++++++++++++++++++++++++
4 files changed, 194 insertions(+)

--- /dev/null
+++ a/include/linux/ptdump.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_PTDUMP_H
+#define _LINUX_PTDUMP_H
+
+#include <linux/mm_types.h>
+
+struct ptdump_range {
+ unsigned long start;
+ unsigned long end;
+};
+
+struct ptdump_state {
+ void (*note_page)(struct ptdump_state *st, unsigned long addr,
+ int level, unsigned long val);
+ const struct ptdump_range *range;
+};
+
+void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm);
+
+#endif /* _LINUX_PTDUMP_H */
--- a/mm/Kconfig.debug~mm-add-generic-ptdump
+++ a/mm/Kconfig.debug
@@ -117,3 +117,24 @@ config DEBUG_RODATA_TEST
depends on STRICT_KERNEL_RWX
---help---
This option enables a testcase for the setting rodata read-only.
+
+config GENERIC_PTDUMP
+ bool
+
+config PTDUMP_CORE
+ bool
+
+config PTDUMP_DEBUGFS
+ bool "Export kernel pagetable layout to userspace via debugfs"
+ depends on DEBUG_KERNEL
+ depends on DEBUG_FS
+ depends on GENERIC_PTDUMP
+ select PTDUMP_CORE
+ 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.
--- a/mm/Makefile~mm-add-generic-ptdump
+++ a/mm/Makefile
@@ -98,6 +98,7 @@ obj-$(CONFIG_CMA) += cma.o
obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o
obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
+obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
obj-$(CONFIG_FRAME_VECTOR) += frame_vector.o
--- /dev/null
+++ a/mm/ptdump.c
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/pagewalk.h>
+#include <linux/ptdump.h>
+#include <linux/kasan.h>
+
+static int ptdump_pgd_entry(pgd_t *pgd, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+ pgd_t val = READ_ONCE(*pgd);
+
+ if (pgd_leaf(val))
+ st->note_page(st, addr, 1, pgd_val(val));
+
+ return 0;
+}
+
+static int ptdump_p4d_entry(p4d_t *p4d, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+ p4d_t val = READ_ONCE(*p4d);
+
+ if (p4d_leaf(val))
+ st->note_page(st, addr, 2, p4d_val(val));
+
+ return 0;
+}
+
+static int ptdump_pud_entry(pud_t *pud, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+ pud_t val = READ_ONCE(*pud);
+
+ if (pud_leaf(val))
+ st->note_page(st, addr, 3, pud_val(val));
+
+ return 0;
+}
+
+static int ptdump_pmd_entry(pmd_t *pmd, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+ pmd_t val = READ_ONCE(*pmd);
+
+ if (pmd_leaf(val))
+ st->note_page(st, addr, 4, pmd_val(val));
+
+ return 0;
+}
+
+static int ptdump_pte_entry(pte_t *pte, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+
+ st->note_page(st, addr, 5, pte_val(READ_ONCE(*pte)));
+
+ return 0;
+}
+
+#ifdef CONFIG_KASAN
+/*
+ * This is an optimization for KASAN=y case. Since all kasan page tables
+ * eventually point to the kasan_early_shadow_page we could call note_page()
+ * right away without walking through lower level page tables. This saves
+ * us dozens of seconds (minutes for 5-level config) while checking for
+ * W+X mapping or reading kernel_page_tables debugfs file.
+ */
+static inline int note_kasan_page_table(struct mm_walk *walk,
+ unsigned long addr)
+{
+ struct ptdump_state *st = walk->private;
+
+ st->note_page(st, addr, 5, pte_val(kasan_early_shadow_pte[0]));
+ return 1;
+}
+
+static int ptdump_test_p4d(unsigned long addr, unsigned long next,
+ p4d_t *p4d, struct mm_walk *walk)
+{
+#if CONFIG_PGTABLE_LEVELS > 4
+ if (p4d == lm_alias(kasan_early_shadow_p4d))
+ return note_kasan_page_table(walk, addr);
+#endif
+ return 0;
+}
+
+static int ptdump_test_pud(unsigned long addr, unsigned long next,
+ pud_t *pud, struct mm_walk *walk)
+{
+#if CONFIG_PGTABLE_LEVELS > 3
+ if (pud == lm_alias(kasan_early_shadow_pud))
+ return note_kasan_page_table(walk, addr);
+#endif
+ return 0;
+}
+
+static int ptdump_test_pmd(unsigned long addr, unsigned long next,
+ pmd_t *pmd, struct mm_walk *walk)
+{
+#if CONFIG_PGTABLE_LEVELS > 2
+ if (pmd == lm_alias(kasan_early_shadow_pmd))
+ return note_kasan_page_table(walk, addr);
+#endif
+ return 0;
+}
+#endif /* CONFIG_KASAN */
+
+static int ptdump_hole(unsigned long addr, unsigned long next,
+ int depth, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+
+ st->note_page(st, addr, depth + 1, 0);
+
+ return 0;
+}
+
+static const struct mm_walk_ops ptdump_ops = {
+ .pgd_entry = ptdump_pgd_entry,
+ .p4d_entry = ptdump_p4d_entry,
+ .pud_entry = ptdump_pud_entry,
+ .pmd_entry = ptdump_pmd_entry,
+ .pte_entry = ptdump_pte_entry,
+#ifdef CONFIG_KASAN
+ .test_p4d = ptdump_test_p4d,
+ .test_pud = ptdump_test_pud,
+ .test_pmd = ptdump_test_pmd,
+#endif
+ .pte_hole = ptdump_hole,
+};
+
+void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)
+{
+ const struct ptdump_range *range = st->range;
+
+ down_read(&mm->mmap_sem);
+ while (range->start != range->end) {
+ walk_page_range_novma(mm, range->start, range->end,
+ &ptdump_ops, st);
+ range++;
+ }
+ up_read(&mm->mmap_sem);
+
+ /* Flush out the last page */
+ st->note_page(st, 0, 0, 0);
+}
_