[PATCH v3 0/5] cleanup page poisoning

[PATCH v3 0/5] cleanup page poisoning

[Vlastimil Babka]

Changes since v2 [2]

- rebase to next-20201113
- apply review feedback from David
- acks from David and Rafael (thanks!)

The first version was called "optimize handling of memory debugging parameters"
[1], changes are:

- apply review feedback
- drop former Patch 3
- add new patches 3-5, change name and cover letter of series

I have identified a number of issues and opportunities for cleanup with
CONFIG_PAGE_POISON and friends:
- interaction with init_on_alloc and init_on_free parameters depends on
  the order of parameters (Patch 1)
- the boot time enabling uses static key, but inefficienty (Patch 2)
- sanity checking is incompatible with hibernation (Patch 3)
- CONFIG_PAGE_POISONING_NO_SANITY can be removed now that we have init_on_free
  (Patch 4)
- CONFIG_PAGE_POISONING_ZERO can be most likely removed now that we have
  init_on_free (Patch 5)

[1] https://lore.kernel.org/r/20201026173358.14704-1-vbabka@suse.cz
[2] https://lore.kernel.org/linux-mm/20201103152237.9853-1-vbabka@suse.cz/

Vlastimil Babka (5):
  mm, page_alloc: do not rely on the order of page_poison and
    init_on_alloc/free parameters
  mm, page_poison: use static key more efficiently
  kernel/power: allow hibernation with page_poison sanity checking
  mm, page_poison: remove CONFIG_PAGE_POISONING_NO_SANITY
  mm, page_poison: remove CONFIG_PAGE_POISONING_ZERO

 drivers/virtio/virtio_balloon.c |   4 +-
 include/linux/mm.h              |  54 +++++++++------
 include/linux/poison.h          |   4 --
 init/main.c                     |   2 +-
 kernel/power/hibernate.c        |   2 +-
 kernel/power/power.h            |   2 +-
 kernel/power/snapshot.c         |  14 +++-
 mm/Kconfig.debug                |  28 ++------
 mm/page_alloc.c                 | 112 ++++++++++++++++----------------
 mm/page_poison.c                |  56 ++--------------
 tools/include/linux/poison.h    |   6 +-
 11 files changed, 117 insertions(+), 167 deletions(-)

-- 
2.29.2

[PATCH v3 1/5] mm, page_alloc: do not rely on the order of page_poison and init_on_alloc/free parameters

[Vlastimil Babka]

Enabling page_poison=1 together with init_on_alloc=1 or init_on_free=1 produces
a warning in dmesg that page_poison takes precedence. However, as these
warnings are printed in early_param handlers for init_on_alloc/free, they are
not printed if page_poison is enabled later on the command line (handlers are
called in the order of their parameters), or when init_on_alloc/free is always
enabled by the respective config option - before the page_poison early param
handler is called, it is not considered to be enabled. This is inconsistent.

We can remove the dependency on order by making the init_on_* parameters only
set a boolean variable, and postponing the evaluation after all early params
have been processed. Introduce a new init_mem_debugging_and_hardening()
function for that, and move the related debug_pagealloc processing there as
well.

As a result init_mem_debugging_and_hardening() knows always accurately if
init_on_* and/or page_poison options were enabled. Thus we can also optimize
want_init_on_alloc() and want_init_on_free(). We don't need to check
page_poisoning_enabled() there, we can instead not enable the init_on_* static
keys at all, if page poisoning is enabled. This results in a simpler and more
effective code.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
---
 include/linux/mm.h | 20 ++---------
 init/main.c        |  2 +-
 mm/page_alloc.c    | 88 ++++++++++++++++++++++------------------------
 3 files changed, 46 insertions(+), 64 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 24f47e140a4c..82ab5c894d94 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2860,6 +2860,7 @@ extern int apply_to_existing_page_range(struct mm_struct *mm,
 				   unsigned long address, unsigned long size,
 				   pte_fn_t fn, void *data);
 
+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);
@@ -2869,35 +2870,20 @@ static inline void kernel_poison_pages(struct page *page, int numpages,
 					int enable) { }
 #endif
 
-#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
-DECLARE_STATIC_KEY_TRUE(init_on_alloc);
-#else
 DECLARE_STATIC_KEY_FALSE(init_on_alloc);
-#endif
 static inline bool want_init_on_alloc(gfp_t flags)
 {
-	if (static_branch_unlikely(&init_on_alloc) &&
-	    !page_poisoning_enabled())
+	if (static_branch_unlikely(&init_on_alloc))
 		return true;
 	return flags & __GFP_ZERO;
 }
 
-#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
-DECLARE_STATIC_KEY_TRUE(init_on_free);
-#else
 DECLARE_STATIC_KEY_FALSE(init_on_free);
-#endif
 static inline bool want_init_on_free(void)
 {
-	return static_branch_unlikely(&init_on_free) &&
-	       !page_poisoning_enabled();
+	return static_branch_unlikely(&init_on_free);
 }
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
-extern void init_debug_pagealloc(void);
-#else
-static inline void init_debug_pagealloc(void) {}
-#endif
 extern bool _debug_pagealloc_enabled_early;
 DECLARE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
 
diff --git a/init/main.c b/init/main.c
index 7262d0a8861b..524089384155 100644
--- a/init/main.c
+++ b/init/main.c
@@ -816,7 +816,7 @@ static void __init mm_init(void)
 	 * bigger than MAX_ORDER unless SPARSEMEM.
 	 */
 	page_ext_init_flatmem();
-	init_debug_pagealloc();
+	init_mem_debugging_and_hardening();
 	kfence_alloc_pool();
 	report_meminit();
 	mem_init();
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 63d8d8b72c10..567060c2ad83 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -165,53 +165,26 @@ unsigned long totalcma_pages __read_mostly;
 
 int percpu_pagelist_fraction;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
-#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
-DEFINE_STATIC_KEY_TRUE(init_on_alloc);
-#else
 DEFINE_STATIC_KEY_FALSE(init_on_alloc);
-#endif
 EXPORT_SYMBOL(init_on_alloc);
 
-#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
-DEFINE_STATIC_KEY_TRUE(init_on_free);
-#else
 DEFINE_STATIC_KEY_FALSE(init_on_free);
-#endif
 EXPORT_SYMBOL(init_on_free);
 
+static bool _init_on_alloc_enabled_early __read_mostly
+				= IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON);
 static int __init early_init_on_alloc(char *buf)
 {
-	int ret;
-	bool bool_result;
 
-	ret = kstrtobool(buf, &bool_result);
-	if (ret)
-		return ret;
-	if (bool_result && page_poisoning_enabled())
-		pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n");
-	if (bool_result)
-		static_branch_enable(&init_on_alloc);
-	else
-		static_branch_disable(&init_on_alloc);
-	return 0;
+	return kstrtobool(buf, &_init_on_alloc_enabled_early);
 }
 early_param("init_on_alloc", early_init_on_alloc);
 
+static bool _init_on_free_enabled_early __read_mostly
+				= IS_ENABLED(CONFIG_INIT_ON_FREE_DEFAULT_ON);
 static int __init early_init_on_free(char *buf)
 {
-	int ret;
-	bool bool_result;
-
-	ret = kstrtobool(buf, &bool_result);
-	if (ret)
-		return ret;
-	if (bool_result && page_poisoning_enabled())
-		pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n");
-	if (bool_result)
-		static_branch_enable(&init_on_free);
-	else
-		static_branch_disable(&init_on_free);
-	return 0;
+	return kstrtobool(buf, &_init_on_free_enabled_early);
 }
 early_param("init_on_free", early_init_on_free);
 
@@ -728,19 +701,6 @@ static int __init early_debug_pagealloc(char *buf)
 }
 early_param("debug_pagealloc", early_debug_pagealloc);
 
-void init_debug_pagealloc(void)
-{
-	if (!debug_pagealloc_enabled())
-		return;
-
-	static_branch_enable(&_debug_pagealloc_enabled);
-
-	if (!debug_guardpage_minorder())
-		return;
-
-	static_branch_enable(&_debug_guardpage_enabled);
-}
-
 static int __init debug_guardpage_minorder_setup(char *buf)
 {
 	unsigned long res;
@@ -792,6 +752,42 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
 				unsigned int order, int migratetype) {}
 #endif
 
+/*
+ * Enable static keys related to various memory debugging and hardening options.
+ * Some override others, and depend on early params that are evaluated in the
+ * order of appearance. So we need to first gather the full picture of what was
+ * enabled, and then make decisions.
+ */
+void init_mem_debugging_and_hardening(void)
+{
+	if (_init_on_alloc_enabled_early) {
+		if (page_poisoning_enabled())
+			pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
+				"will take precedence over init_on_alloc\n");
+		else
+			static_branch_enable(&init_on_alloc);
+	}
+	if (_init_on_free_enabled_early) {
+		if (page_poisoning_enabled())
+			pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
+				"will take precedence over init_on_free\n");
+		else
+			static_branch_enable(&init_on_free);
+	}
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+	if (!debug_pagealloc_enabled())
+		return;
+
+	static_branch_enable(&_debug_pagealloc_enabled);
+
+	if (!debug_guardpage_minorder())
+		return;
+
+	static_branch_enable(&_debug_guardpage_enabled);
+#endif
+}
+
 static inline void set_buddy_order(struct page *page, unsigned int order)
 {
 	set_page_private(page, order);
-- 
2.29.2

[PATCH v3 2/5] mm, page_poison: use static key more efficiently

[Vlastimil Babka]

Commit 11c9c7edae06 ("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().

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 drivers/virtio/virtio_balloon.c |  2 +-
 include/linux/mm.h              | 33 +++++++++++++++++---
 mm/page_alloc.c                 | 18 +++++++++--
 mm/page_poison.c                | 53 +++++----------------------------
 4 files changed, 52 insertions(+), 54 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 481611c09dae..e53faed6ba93 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -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);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 82ab5c894d94..5ab5358be2b3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2862,12 +2862,37 @@ 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);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 567060c2ad83..cd966829bed3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -775,6 +775,17 @@ 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
@@ -2217,7 +2229,7 @@ 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
@@ -2279,7 +2291,7 @@ 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);
 }
 
diff --git a/mm/page_poison.c b/mm/page_poison.c
index e6c994af7518..0d899a01d107 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -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)
 {
-- 
2.29.2

[PATCH v3 3/5] kernel/power: allow hibernation with page_poison sanity checking

[Vlastimil Babka]

Page poisoning used to be incompatible with hibernation, as the state of
poisoned pages was lost after resume, thus enabling CONFIG_HIBERNATION forces
CONFIG_PAGE_POISONING_NO_SANITY. For the same reason, the poisoning with zeroes
variant CONFIG_PAGE_POISONING_ZERO used to disable hibernation. The latter
restriction was removed by commit 1ad1410f632d ("PM / Hibernate: allow
hibernation with PAGE_POISONING_ZERO") and similarly for init_on_free by commit
18451f9f9e58 ("PM: hibernate: fix crashes with init_on_free=1") by making sure
free pages are cleared after resume.

We can use the same mechanism to instead poison free pages with PAGE_POISON
after resume. This covers both zero and 0xAA patterns. Thus we can remove the
Kconfig restriction that disables page poison sanity checking when hibernation
is enabled.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> # for hibernation
---
 include/linux/mm.h       |  1 +
 kernel/power/hibernate.c |  2 +-
 kernel/power/power.h     |  2 +-
 kernel/power/snapshot.c  | 14 +++++++++++---
 mm/Kconfig.debug         |  1 -
 5 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5ab5358be2b3..b15000085ff2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2891,6 +2891,7 @@ static inline void kernel_unpoison_pages(struct page *page, int numpages)
 #else
 static inline bool page_poisoning_enabled(void) { return false; }
 static inline bool page_poisoning_enabled_static(void) { return false; }
+static inline void __kernel_poison_pages(struct page *page, int nunmpages) { }
 static inline void kernel_poison_pages(struct page *page, int numpages) { }
 static inline void kernel_unpoison_pages(struct page *page, int numpages) { }
 #endif
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index d5d48404db37..559acef3fddb 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -329,7 +329,7 @@ static int create_image(int platform_mode)
 
 	if (!in_suspend) {
 		events_check_enabled = false;
-		clear_free_pages();
+		clear_or_poison_free_pages();
 	}
 
 	platform_leave(platform_mode);
diff --git a/kernel/power/power.h b/kernel/power/power.h
index 24f12d534515..778bf431ec02 100644
--- a/kernel/power/power.h
+++ b/kernel/power/power.h
@@ -106,7 +106,7 @@ extern int create_basic_memory_bitmaps(void);
 extern void free_basic_memory_bitmaps(void);
 extern int hibernate_preallocate_memory(void);
 
-extern void clear_free_pages(void);
+extern void clear_or_poison_free_pages(void);
 
 /**
  *	Auxiliary structure used for reading the snapshot image data and
diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index af534982062d..64b7aab9aee4 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1178,7 +1178,15 @@ void free_basic_memory_bitmaps(void)
 	pr_debug("Basic memory bitmaps freed\n");
 }
 
-void clear_free_pages(void)
+static void clear_or_poison_free_page(struct page *page)
+{
+	if (page_poisoning_enabled_static())
+		__kernel_poison_pages(page, 1);
+	else if (want_init_on_free())
+		clear_highpage(page);
+}
+
+void clear_or_poison_free_pages(void)
 {
 	struct memory_bitmap *bm = free_pages_map;
 	unsigned long pfn;
@@ -1186,12 +1194,12 @@ void clear_free_pages(void)
 	if (WARN_ON(!(free_pages_map)))
 		return;
 
-	if (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) || want_init_on_free()) {
+	if (page_poisoning_enabled() || want_init_on_free()) {
 		memory_bm_position_reset(bm);
 		pfn = memory_bm_next_pfn(bm);
 		while (pfn != BM_END_OF_MAP) {
 			if (pfn_valid(pfn))
-				clear_highpage(pfn_to_page(pfn));
+				clear_or_poison_free_page(pfn_to_page(pfn));
 
 			pfn = memory_bm_next_pfn(bm);
 		}
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 864f129f1937..c57786ad5be9 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -64,7 +64,6 @@ config PAGE_OWNER
 
 config PAGE_POISONING
 	bool "Poison pages after freeing"
-	select PAGE_POISONING_NO_SANITY if HIBERNATION
 	help
 	  Fill the pages with poison patterns after free_pages() and verify
 	  the patterns before alloc_pages. The filling of the memory helps
-- 
2.29.2

[PATCH v3 4/5] mm, page_poison: remove CONFIG_PAGE_POISONING_NO_SANITY

[Vlastimil Babka]

CONFIG_PAGE_POISONING_NO_SANITY skips the check on page alloc whether the
poison pattern was corrupted, suggesting a use-after-free. The motivation to
introduce it in commit 8823b1dbc05f ("mm/page_poison.c: enable PAGE_POISONING
as a separate option") was to simply sanitize freed pages, optimally together
with CONFIG_PAGE_POISONING_ZERO.

These days we have an init_on_free=1 boot option, which makes this use case of
page poisoning redundant. For sanitizing, writing zeroes is sufficient, there
is pretty much no benefit from writing the 0xAA poison pattern to freed pages,
without checking it back on alloc. Thus, remove this option and suggest
init_on_free instead in the main config's help.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/virtio_balloon.c |  4 +---
 mm/Kconfig.debug                | 15 ++++-----------
 mm/page_poison.c                |  3 ---
 3 files changed, 5 insertions(+), 17 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index e53faed6ba93..8985fc2cea86 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -1114,9 +1114,7 @@ static int virtballoon_validate(struct virtio_device *vdev)
 	 * page reporting as it could potentially change the contents
 	 * of our free pages.
 	 */
-	if (!want_init_on_free() &&
-	    (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) ||
-	     !page_poisoning_enabled_static()))
+	if (!want_init_on_free() && !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);
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index c57786ad5be9..14e29fe5bfa6 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -74,18 +74,11 @@ config PAGE_POISONING
 	  Note that "poison" here is not the same thing as the "HWPoison"
 	  for CONFIG_MEMORY_FAILURE. This is software poisoning only.
 
-	  If unsure, say N
+	  If you are only interested in sanitization of freed pages without
+	  checking the poison pattern on alloc, you can boot the kernel with
+	  "init_on_free=1" instead of enabling this.
 
-config PAGE_POISONING_NO_SANITY
-	depends on PAGE_POISONING
-	bool "Only poison, don't sanity check"
-	help
-	   Skip the sanity checking on alloc, only fill the pages with
-	   poison on free. This reduces some of the overhead of the
-	   poisoning feature.
-
-	   If you are only interested in sanitization, say Y. Otherwise
-	   say N.
+	  If unsure, say N
 
 config PAGE_POISONING_ZERO
 	bool "Use zero for poisoning instead of debugging value"
diff --git a/mm/page_poison.c b/mm/page_poison.c
index 0d899a01d107..65cdf844c8ad 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -51,9 +51,6 @@ static void check_poison_mem(unsigned char *mem, size_t bytes)
 	unsigned char *start;
 	unsigned char *end;
 
-	if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
-		return;
-
 	start = memchr_inv(mem, PAGE_POISON, bytes);
 	if (!start)
 		return;
-- 
2.29.2

[PATCH v3 5/5] mm, page_poison: remove CONFIG_PAGE_POISONING_ZERO

[Vlastimil Babka]

CONFIG_PAGE_POISONING_ZERO uses the zero pattern instead of 0xAA. It was
introduced by commit 1414c7f4f7d7 ("mm/page_poisoning.c: allow for zero
poisoning"), noting that using zeroes retains the benefit of sanitizing content
of freed pages, with the benefit of not having to zero them again on alloc, and
the downside of making some forms of corruption (stray writes of NULLs) harder
to detect than with the 0xAA pattern. Together with
CONFIG_PAGE_POISONING_NO_SANITY it made possible to sanitize the contents on
free without checking it back on alloc.

These days we have the init_on_free() option to achieve sanitization with
zeroes and to save clearing on alloc (and without checking on alloc). Arguably
if someone does choose to check the poison for corruption on alloc, the savings
of not clearing the page are secondary, and it makes sense to always use the
0xAA poison pattern. Thus, remove the CONFIG_PAGE_POISONING_ZERO option for
being redundant.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
---
 include/linux/poison.h       |  4 ----
 mm/Kconfig.debug             | 12 ------------
 mm/page_alloc.c              |  8 +-------
 tools/include/linux/poison.h |  6 +-----
 4 files changed, 2 insertions(+), 28 deletions(-)

diff --git a/include/linux/poison.h b/include/linux/poison.h
index dc8ae5d8db03..aff1c9250c82 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -27,11 +27,7 @@
 #define TIMER_ENTRY_STATIC	((void *) 0x300 + POISON_POINTER_DELTA)
 
 /********** mm/page_poison.c **********/
-#ifdef CONFIG_PAGE_POISONING_ZERO
-#define PAGE_POISON 0x00
-#else
 #define PAGE_POISON 0xaa
-#endif
 
 /********** mm/page_alloc.c ************/
 
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 14e29fe5bfa6..1e73717802f8 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -80,18 +80,6 @@ config PAGE_POISONING
 
 	  If unsure, say N
 
-config PAGE_POISONING_ZERO
-	bool "Use zero for poisoning instead of debugging value"
-	depends on PAGE_POISONING
-	help
-	   Instead of using the existing poison value, fill the pages with
-	   zeros. This makes it harder to detect when errors are occurring
-	   due to sanitization but the zeroing at free means that it is
-	   no longer necessary to write zeros when GFP_ZERO is used on
-	   allocation.
-
-	   If unsure, say N
-
 config DEBUG_PAGE_REF
 	bool "Enable tracepoint to track down page reference manipulation"
 	depends on DEBUG_KERNEL
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cd966829bed3..e80d5ce1b292 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2226,12 +2226,6 @@ static inline int check_new_page(struct page *page)
 	return 1;
 }
 
-static inline bool free_pages_prezeroed(void)
-{
-	return (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
-		page_poisoning_enabled_static()) || want_init_on_free();
-}
-
 #ifdef CONFIG_DEBUG_VM
 /*
  * With DEBUG_VM enabled, order-0 pages are checked for expected state when
@@ -2300,7 +2294,7 @@ static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags
 {
 	post_alloc_hook(page, order, gfp_flags);
 
-	if (!free_pages_prezeroed() && want_init_on_alloc(gfp_flags))
+	if (!want_init_on_free() && want_init_on_alloc(gfp_flags))
 		kernel_init_free_pages(page, 1 << order);
 
 	if (order && (gfp_flags & __GFP_COMP))
diff --git a/tools/include/linux/poison.h b/tools/include/linux/poison.h
index d29725769107..2e6338ac5eed 100644
--- a/tools/include/linux/poison.h
+++ b/tools/include/linux/poison.h
@@ -35,12 +35,8 @@
  */
 #define TIMER_ENTRY_STATIC	((void *) 0x300 + POISON_POINTER_DELTA)
 
-/********** mm/debug-pagealloc.c **********/
-#ifdef CONFIG_PAGE_POISONING_ZERO
-#define PAGE_POISON 0x00
-#else
+/********** mm/page_poison.c **********/
 #define PAGE_POISON 0xaa
-#endif
 
 /********** mm/page_alloc.c ************/
 
-- 
2.29.2

Re: [PATCH v3 2/5] mm, page_poison: use static key more efficiently

[David Hildenbrand]

On 13.11.20 11:40, Vlastimil Babka wrote:
> Commit 11c9c7edae06 ("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().
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>   drivers/virtio/virtio_balloon.c |  2 +-
>   include/linux/mm.h              | 33 +++++++++++++++++---
>   mm/page_alloc.c                 | 18 +++++++++--
>   mm/page_poison.c                | 53 +++++----------------------------
>   4 files changed, 52 insertions(+), 54 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 481611c09dae..e53faed6ba93 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -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);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 82ab5c894d94..5ab5358be2b3 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2862,12 +2862,37 @@ 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);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 567060c2ad83..cd966829bed3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -775,6 +775,17 @@ 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
> @@ -2217,7 +2229,7 @@ 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
> @@ -2279,7 +2291,7 @@ 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);
>   }
>   
> diff --git a/mm/page_poison.c b/mm/page_poison.c
> index e6c994af7518..0d899a01d107 100644
> --- a/mm/page_poison.c
> +++ b/mm/page_poison.c
> @@ -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)
>   {
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb

Re: [PATCH v3 3/5] kernel/power: allow hibernation with page_poison sanity checking

[David Hildenbrand]

On 13.11.20 11:40, Vlastimil Babka wrote:
> Page poisoning used to be incompatible with hibernation, as the state of
> poisoned pages was lost after resume, thus enabling CONFIG_HIBERNATION forces
> CONFIG_PAGE_POISONING_NO_SANITY. For the same reason, the poisoning with zeroes
> variant CONFIG_PAGE_POISONING_ZERO used to disable hibernation. The latter
> restriction was removed by commit 1ad1410f632d ("PM / Hibernate: allow
> hibernation with PAGE_POISONING_ZERO") and similarly for init_on_free by commit
> 18451f9f9e58 ("PM: hibernate: fix crashes with init_on_free=1") by making sure
> free pages are cleared after resume.
> 
> We can use the same mechanism to instead poison free pages with PAGE_POISON
> after resume. This covers both zero and 0xAA patterns. Thus we can remove the
> Kconfig restriction that disables page poison sanity checking when hibernation
> is enabled.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> # for hibernation
> ---
>   include/linux/mm.h       |  1 +
>   kernel/power/hibernate.c |  2 +-
>   kernel/power/power.h     |  2 +-
>   kernel/power/snapshot.c  | 14 +++++++++++---
>   mm/Kconfig.debug         |  1 -
>   5 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5ab5358be2b3..b15000085ff2 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2891,6 +2891,7 @@ static inline void kernel_unpoison_pages(struct page *page, int numpages)
>   #else
>   static inline bool page_poisoning_enabled(void) { return false; }
>   static inline bool page_poisoning_enabled_static(void) { return false; }
> +static inline void __kernel_poison_pages(struct page *page, int nunmpages) { }
>   static inline void kernel_poison_pages(struct page *page, int numpages) { }
>   static inline void kernel_unpoison_pages(struct page *page, int numpages) { }
>   #endif
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index d5d48404db37..559acef3fddb 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -329,7 +329,7 @@ static int create_image(int platform_mode)
>   
>   	if (!in_suspend) {
>   		events_check_enabled = false;
> -		clear_free_pages();
> +		clear_or_poison_free_pages();
>   	}
>   
>   	platform_leave(platform_mode);
> diff --git a/kernel/power/power.h b/kernel/power/power.h
> index 24f12d534515..778bf431ec02 100644
> --- a/kernel/power/power.h
> +++ b/kernel/power/power.h
> @@ -106,7 +106,7 @@ extern int create_basic_memory_bitmaps(void);
>   extern void free_basic_memory_bitmaps(void);
>   extern int hibernate_preallocate_memory(void);
>   
> -extern void clear_free_pages(void);
> +extern void clear_or_poison_free_pages(void);
>   
>   /**
>    *	Auxiliary structure used for reading the snapshot image data and
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index af534982062d..64b7aab9aee4 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -1178,7 +1178,15 @@ void free_basic_memory_bitmaps(void)
>   	pr_debug("Basic memory bitmaps freed\n");
>   }
>   
> -void clear_free_pages(void)
> +static void clear_or_poison_free_page(struct page *page)
> +{
> +	if (page_poisoning_enabled_static())
> +		__kernel_poison_pages(page, 1);
> +	else if (want_init_on_free())
> +		clear_highpage(page);
> +}
> +
> +void clear_or_poison_free_pages(void)
>   {
>   	struct memory_bitmap *bm = free_pages_map;
>   	unsigned long pfn;
> @@ -1186,12 +1194,12 @@ void clear_free_pages(void)
>   	if (WARN_ON(!(free_pages_map)))
>   		return;
>   
> -	if (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) || want_init_on_free()) {
> +	if (page_poisoning_enabled() || want_init_on_free()) {

Any reason why not to use the static version here?

Reviewed-by: David Hildenbrand <david@redhat.com>


-- 
Thanks,

David / dhildenb

Re: [PATCH v3 3/5] kernel/power: allow hibernation with page_poison sanity checking

[Vlastimil Babka]

On 11/13/20 1:10 PM, David Hildenbrand wrote:
>> @@ -1186,12 +1194,12 @@ void clear_free_pages(void)
>>   	if (WARN_ON(!(free_pages_map)))
>>   		return;
>>   
>> -	if (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) || want_init_on_free()) {
>> +	if (page_poisoning_enabled() || want_init_on_free()) {
> 
> Any reason why not to use the static version here?

It's a single check per resume, so not worth live-patching this place.

> Reviewed-by: David Hildenbrand <david@redhat.com>
> 
> 

Re: [PATCH v3 3/5] kernel/power: allow hibernation with page_poison sanity checking

[David Hildenbrand]

On 13.11.20 13:15, Vlastimil Babka wrote:
> On 11/13/20 1:10 PM, David Hildenbrand wrote:
>>> @@ -1186,12 +1194,12 @@ void clear_free_pages(void)
>>>    	if (WARN_ON(!(free_pages_map)))
>>>    		return;
>>>    
>>> -	if (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) || want_init_on_free()) {
>>> +	if (page_poisoning_enabled() || want_init_on_free()) {
>>
>> Any reason why not to use the static version here?
> 
> It's a single check per resume, so not worth live-patching this place.

Agreed, thanks.


-- 
Thanks,

David / dhildenb