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>

1 files changed, 29 insertions, 4 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 591c784277ea..026707a58159 100644
--- 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);