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x86/mm/dump_pagetables: Speed up page tables dump for CONFIG_KASAN=y 

KASAN fills kernel page tables with repeated values to map several
TBs of the virtual memory to the single kasan_zero_page:
  kasan_zero_p4d ->
    kasan_zero_pud ->
        kasan_zero_pmd->
            kasan_zero_pte->
                kasan_zero_page

Walking the whole KASAN shadow range takes a lot of time, especially
with 5-level page tables. Since we already know that all kasan page tables
eventually point to the kasan_zero_page we could call note_page()
right and avoid walking lower levels of the page tables.
This will not affect the output of the kernel_page_tables file,
but let us avoid spending time in page table walkers:

Before:

  $ time cat /sys/kernel/debug/kernel_page_tables > /dev/null

  real    0m55.855s
  user    0m0.000s
  sys     0m55.840s

After:

  $ time cat /sys/kernel/debug/kernel_page_tables > /dev/null

  real    0m0.054s
  user    0m0.000s
  sys     0m0.054s

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170724152558.24689-1-aryabinin@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andrey Ryabinin 2017-07-24 18:25:58 +03:00 committed by Ingo Molnar
parent 10af6235e0
commit 04b67022fb
1 changed files with 41 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

64
arch/x86/mm/dump_pagetables.c
View File

@ -13,12 +13,12 @@
*/
#include <linux/debugfs.h>
#include <linux/kasan.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <asm/kasan.h>
#include <asm/pgtable.h>
/*
@ -302,23 +302,53 @@ static void walk_pte_level(struct seq_file *m, struct pg_state *st, pmd_t addr,
start++;
}
}
#ifdef CONFIG_KASAN
/*
* This is an optimization for KASAN=y case. Since all kasan page tables
* eventually point to the kasan_zero_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 bool kasan_page_table(struct seq_file *m, struct pg_state *st,
void *pt)
{
if (__pa(pt) == __pa(kasan_zero_pmd) ||
#ifdef CONFIG_X86_5LEVEL
__pa(pt) == __pa(kasan_zero_p4d) ||
#endif
__pa(pt) == __pa(kasan_zero_pud)) {
pgprotval_t prot = pte_flags(kasan_zero_pte[0]);
note_page(m, st, __pgprot(prot), 5);
return true;
}
return false;
}
#else
static inline bool kasan_page_table(struct seq_file *m, struct pg_state *st,
void *pt)
{
return false;
}
#endif
#if PTRS_PER_PMD > 1
static void walk_pmd_level(struct seq_file *m, struct pg_state *st, pud_t addr, unsigned long P)
{
int i;
pmd_t *start;
pmd_t *start, *pmd_start;
pgprotval_t prot;
start = (pmd_t *)pud_page_vaddr(addr);
pmd_start = start = (pmd_t *)pud_page_vaddr(addr);
for (i = 0; i < PTRS_PER_PMD; i++) {
st->current_address = normalize_addr(P + i * PMD_LEVEL_MULT);
if (!pmd_none(*start)) {
if (pmd_large(*start) || !pmd_present(*start)) {
prot = pmd_flags(*start);
note_page(m, st, __pgprot(prot), 4);
} else {
} else if (!kasan_page_table(m, st, pmd_start)) {
walk_pte_level(m, st, *start,
P + i * PMD_LEVEL_MULT);
}
@ -336,34 +366,22 @@ static void walk_pmd_level(struct seq_file *m, struct pg_state *st, pud_t addr,
#if PTRS_PER_PUD > 1
/*
* This is an optimization for CONFIG_DEBUG_WX=y + CONFIG_KASAN=y
* KASAN fills page tables with the same values. Since there is no
* point in checking page table more than once we just skip repeated
* entries. This saves us dozens of seconds during boot.
*/
static bool pud_already_checked(pud_t *prev_pud, pud_t *pud, bool checkwx)
{
return checkwx && prev_pud && (pud_val(*prev_pud) == pud_val(*pud));
}
static void walk_pud_level(struct seq_file *m, struct pg_state *st, p4d_t addr, unsigned long P)
{
int i;
pud_t *start;
pud_t *start, *pud_start;
pgprotval_t prot;
pud_t *prev_pud = NULL;
start = (pud_t *)p4d_page_vaddr(addr);
pud_start = start = (pud_t *)p4d_page_vaddr(addr);
for (i = 0; i < PTRS_PER_PUD; i++) {
st->current_address = normalize_addr(P + i * PUD_LEVEL_MULT);
if (!pud_none(*start) &&
!pud_already_checked(prev_pud, start, st->check_wx)) {
if (!pud_none(*start)) {
if (pud_large(*start) || !pud_present(*start)) {
prot = pud_flags(*start);
note_page(m, st, __pgprot(prot), 3);
} else {
} else if (!kasan_page_table(m, st, pud_start)) {
walk_pmd_level(m, st, *start,
P + i * PUD_LEVEL_MULT);
}
@ -386,10 +404,10 @@ static void walk_pud_level(struct seq_file *m, struct pg_state *st, p4d_t addr,
static void walk_p4d_level(struct seq_file *m, struct pg_state *st, pgd_t addr, unsigned long P)
{
int i;
p4d_t *start;
p4d_t *start, *p4d_start;
pgprotval_t prot;
start = (p4d_t *)pgd_page_vaddr(addr);
p4d_start = start = (p4d_t *)pgd_page_vaddr(addr);
for (i = 0; i < PTRS_PER_P4D; i++) {
st->current_address = normalize_addr(P + i * P4D_LEVEL_MULT);
@ -397,7 +415,7 @@ static void walk_p4d_level(struct seq_file *m, struct pg_state *st, pgd_t addr,
if (p4d_large(*start) || !p4d_present(*start)) {
prot = p4d_flags(*start);
note_page(m, st, __pgprot(prot), 2);
} else {
} else if (!kasan_page_table(m, st, p4d_start)) {
walk_pud_level(m, st, *start,
P + i * P4D_LEVEL_MULT);
}