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Enabling both DEBUG_WX=y and KASAN=y options significantly increases boot time (dozens of seconds at least). KASAN fills kernel page tables with repeated values to map several TBs of the virtual memory to the single kasan_zero_page: kasan_zero_pud -> kasan_zero_pmd-> kasan_zero_pte-> kasan_zero_page So, the page table walker used to find W+X mapping check the same kasan_zero_p?d page table entries a lot more than once. With patch pud walker will skip the pud if it has the same value as the previous one . Skipping done iff we search for W+X mappings, so this optimization won't affect the page table dump via debugfs. This dropped time spend in W+X check from ~30 sec to reasonable 0.1 sec: Before: [ 4.579991] Freeing unused kernel memory: 1000K [ 35.257523] x86/mm: Checked W+X mappings: passed, no W+X pages found. After: [ 5.138756] Freeing unused kernel memory: 1000K [ 5.266496] x86/mm: Checked W+X mappings: passed, no W+X pages found. Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Reviewed-by: Alexander Potapenko <glider@google.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: kasan-dev@googlegroups.com Cc: Tobias Regnery <tobias.regnery@gmail.com> Cc: Dmitry Vyukov <dvyukov@google.com> Link: http://lkml.kernel.org/r/20170214100839.17186-1-aryabinin@virtuozzo.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
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.. | ||
boot | ||
configs | ||
crypto | ||
entry | ||
events | ||
ia32 | ||
include | ||
kernel | ||
kvm | ||
lguest | ||
lib | ||
math-emu | ||
mm | ||
net | ||
oprofile | ||
pci | ||
platform | ||
power | ||
purgatory | ||
ras | ||
realmode | ||
tools | ||
um | ||
video | ||
xen | ||
.gitignore | ||
Kbuild | ||
Kconfig | ||
Kconfig.cpu | ||
Kconfig.debug | ||
Makefile | ||
Makefile.um | ||
Makefile_32.cpu |