Commit 8db26a3d authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
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mm, page_poison: use static key more efficiently 

Commit 11c9c7ed ("mm/page_poison.c: replace bool variable with static
key") changed page_poisoning_enabled() to a static key check.  However,
the function is not inlined, so each check still involves a function call
with overhead not eliminated when page poisoning is disabled.

Analogically to how debug_pagealloc is handled, this patch converts
page_poisoning_enabled() back to boolean check, and introduces
page_poisoning_enabled_static() for fast paths.  Both functions are
inlined.

The function kernel_poison_pages() is also called unconditionally and does
the static key check inside.  Remove it from there and put it to callers.
Also split it to two functions kernel_poison_pages() and
kernel_unpoison_pages() instead of the confusing bool parameter.

Also optimize the check that enables page poisoning instead of
debug_pagealloc for architectures without proper debug_pagealloc support.
Move the check to init_mem_debugging_and_hardening() to enable a single
static key instead of having two static branches in
page_poisoning_enabled_static().

Link: https://lkml.kernel.org/r/20201113104033.22907-3-vbabka@suse.cz


Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Laura Abbott <labbott@kernel.org>
Cc: Mateusz Nosek <mateusznosek0@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 04013513

drivers/virtio/virtio_balloon.c

+1 −1
Original line number Diff line number Diff line
@@ -1116,7 +1116,7 @@ static int virtballoon_validate(struct virtio_device *vdev) 
	 */

	if (!want_init_on_free() &&

	    (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) ||

	     !page_poisoning_enabled()))

	     !page_poisoning_enabled_static()))

		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);

	else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))

		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);

include/linux/mm.h

+29 −4
Original line number Diff line number Diff line
@@ -2874,12 +2874,37 @@ extern int apply_to_existing_page_range(struct mm_struct *mm, 


extern void init_mem_debugging_and_hardening(void);

#ifdef CONFIG_PAGE_POISONING

extern bool page_poisoning_enabled(void);

extern void kernel_poison_pages(struct page *page, int numpages, int enable);

extern void __kernel_poison_pages(struct page *page, int numpages);

extern void __kernel_unpoison_pages(struct page *page, int numpages);

extern bool _page_poisoning_enabled_early;

DECLARE_STATIC_KEY_FALSE(_page_poisoning_enabled);

static inline bool page_poisoning_enabled(void)

{

	return _page_poisoning_enabled_early;

}

/*

 * For use in fast paths after init_mem_debugging() has run, or when a

 * false negative result is not harmful when called too early.

 */

static inline bool page_poisoning_enabled_static(void)

{

	return static_branch_unlikely(&_page_poisoning_enabled);

}

static inline void kernel_poison_pages(struct page *page, int numpages)

{

	if (page_poisoning_enabled_static())

		__kernel_poison_pages(page, numpages);

}

static inline void kernel_unpoison_pages(struct page *page, int numpages)

{

	if (page_poisoning_enabled_static())

		__kernel_unpoison_pages(page, numpages);

}

#else

static inline bool page_poisoning_enabled(void) { return false; }

static inline void kernel_poison_pages(struct page *page, int numpages,

					int enable) { }

static inline bool page_poisoning_enabled_static(void) { return false; }

static inline void kernel_poison_pages(struct page *page, int numpages) { }

static inline void kernel_unpoison_pages(struct page *page, int numpages) { }

#endif



DECLARE_STATIC_KEY_FALSE(init_on_alloc);

mm/page_alloc.c

+15 −3
Original line number Diff line number Diff line
@@ -777,6 +777,17 @@ void init_mem_debugging_and_hardening(void) 
			static_branch_enable(&init_on_free);

	}



#ifdef CONFIG_PAGE_POISONING

	/*

	 * Page poisoning is debug page alloc for some arches. If

	 * either of those options are enabled, enable poisoning.

	 */

	if (page_poisoning_enabled() ||

	     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&

	      debug_pagealloc_enabled()))

		static_branch_enable(&_page_poisoning_enabled);

#endif



#ifdef CONFIG_DEBUG_PAGEALLOC

	if (!debug_pagealloc_enabled())

		return;
@@ -1262,7 +1273,8 @@ static __always_inline bool free_pages_prepare(struct page *page, 
	if (want_init_on_free())

		kernel_init_free_pages(page, 1 << order);



	kernel_poison_pages(page, 1 << order, 0);

	kernel_poison_pages(page, 1 << order);



	/*

	 * arch_free_page() can make the page's contents inaccessible.  s390

	 * does this.  So nothing which can access the page's contents should
@@ -2219,7 +2231,7 @@ static inline int check_new_page(struct page *page) 
static inline bool free_pages_prezeroed(void)

{

	return (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&

		page_poisoning_enabled()) || want_init_on_free();

		page_poisoning_enabled_static()) || want_init_on_free();

}



#ifdef CONFIG_DEBUG_VM
@@ -2281,7 +2293,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order, 
	arch_alloc_page(page, order);

	debug_pagealloc_map_pages(page, 1 << order);

	kasan_alloc_pages(page, order);

	kernel_poison_pages(page, 1 << order, 1);

	kernel_unpoison_pages(page, 1 << order);

	set_page_owner(page, order, gfp_flags);



	if (!free_pages_prezeroed() && want_init_on_alloc(gfp_flags))

mm/page_poison.c

+7 −46
Original line number Diff line number Diff line
@@ -8,45 +8,17 @@ 
#include <linux/ratelimit.h>

#include <linux/kasan.h>



static DEFINE_STATIC_KEY_FALSE_RO(want_page_poisoning);

bool _page_poisoning_enabled_early;

EXPORT_SYMBOL(_page_poisoning_enabled_early);

DEFINE_STATIC_KEY_FALSE(_page_poisoning_enabled);

EXPORT_SYMBOL(_page_poisoning_enabled);



static int __init early_page_poison_param(char *buf)

{

	int ret;

	bool tmp;



	ret = strtobool(buf, &tmp);

	if (ret)

		return ret;



	if (tmp)

		static_branch_enable(&want_page_poisoning);

	else

		static_branch_disable(&want_page_poisoning);



	return 0;

	return kstrtobool(buf, &_page_poisoning_enabled_early);

}

early_param("page_poison", early_page_poison_param);



/**

 * page_poisoning_enabled - check if page poisoning is enabled

 *

 * Return true if page poisoning is enabled, or false if not.

 */

bool page_poisoning_enabled(void)

{

	/*

	 * Assumes that debug_pagealloc_enabled is set before

	 * memblock_free_all.

	 * Page poisoning is debug page alloc for some arches. If

	 * either of those options are enabled, enable poisoning.

	 */

	return (static_branch_unlikely(&want_page_poisoning) ||

		(!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&

		debug_pagealloc_enabled()));

}

EXPORT_SYMBOL_GPL(page_poisoning_enabled);



static void poison_page(struct page *page)

{

	void *addr = kmap_atomic(page);
@@ -58,7 +30,7 @@ static void poison_page(struct page *page) 
	kunmap_atomic(addr);

}



static void poison_pages(struct page *page, int n)

void __kernel_poison_pages(struct page *page, int n)

{

	int i;
@@ -117,7 +89,7 @@ static void unpoison_page(struct page *page) 
	kunmap_atomic(addr);

}



static void unpoison_pages(struct page *page, int n)

void __kernel_unpoison_pages(struct page *page, int n)

{

	int i;
@@ -125,17 +97,6 @@ static void unpoison_pages(struct page *page, int n) 
		unpoison_page(page + i);

}



void kernel_poison_pages(struct page *page, int numpages, int enable)

{

	if (!page_poisoning_enabled())

		return;



	if (enable)

		unpoison_pages(page, numpages);

	else

		poison_pages(page, numpages);

}



#ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC

void __kernel_map_pages(struct page *page, int numpages, int enable)

{

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