mm, page_poison: use static key more efficiently

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().

Link: https://lkml.kernel.org/r/20201113104033.22907-3-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: David 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 481611c..e53faed 100644 (file)
--- 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 591c784..026707a 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -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);

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3fd0c8d..efcd1ba 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -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))

diff --git a/mm/page_poison.c b/mm/page_poison.c
index ae0482c..4d75fc9 100644 (file)
--- 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)
 {