From:   andrey.konovalov@linux.dev
To:     Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH mm v4 01/39] kasan, page_alloc: deduplicate should_skip_kasan_poison
Date:   Mon, 20 Dec 2021 22:58:16 +0100
Message-Id: <157f8aec0be7f54666b9cc433a0c0450416b68b4.1640036051.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

Currently, should_skip_kasan_poison() has two definitions: one for when
CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, one for when it's not.

Instead of duplicating the checks, add a deferred_pages_enabled()
helper and use it in a single should_skip_kasan_poison() definition.

Also move should_skip_kasan_poison() closer to its caller and clarify
all conditions in the comment.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v2->v3:
- Update patch description.
---
 mm/page_alloc.c | 55 +++++++++++++++++++++++++++++--------------------
 1 file changed, 33 insertions(+), 22 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index edfd6c81af82..f0bcecac19cd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -377,25 +377,9 @@ int page_group_by_mobility_disabled __read_mostly;
  */
 static DEFINE_STATIC_KEY_TRUE(deferred_pages);
 
-/*
- * Calling kasan_poison_pages() only after deferred memory initialization
- * has completed. Poisoning pages during deferred memory init will greatly
- * lengthen the process and cause problem in large memory systems as the
- * deferred pages initialization is done with interrupt disabled.
- *
- * Assuming that there will be no reference to those newly initialized
- * pages before they are ever allocated, this should have no effect on
- * KASAN memory tracking as the poison will be properly inserted at page
- * allocation time. The only corner case is when pages are allocated by
- * on-demand allocation and then freed again before the deferred pages
- * initialization is done, but this is not likely to happen.
- */
-static inline bool should_skip_kasan_poison(struct page *page, fpi_t fpi_flags)
+static inline bool deferred_pages_enabled(void)
 {
-	return static_branch_unlikely(&deferred_pages) ||
-	       (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
-		(fpi_flags & FPI_SKIP_KASAN_POISON)) ||
-	       PageSkipKASanPoison(page);
+	return static_branch_unlikely(&deferred_pages);
 }
 
 /* Returns true if the struct page for the pfn is uninitialised */
@@ -446,11 +430,9 @@ defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
 	return false;
 }
 #else
-static inline bool should_skip_kasan_poison(struct page *page, fpi_t fpi_flags)
+static inline bool deferred_pages_enabled(void)
 {
-	return (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
-		(fpi_flags & FPI_SKIP_KASAN_POISON)) ||
-	       PageSkipKASanPoison(page);
+	return false;
 }
 
 static inline bool early_page_uninitialised(unsigned long pfn)
@@ -1270,6 +1252,35 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
 	return ret;
 }
 
+/*
+ * Skip KASAN memory poisoning when either:
+ *
+ * 1. Deferred memory initialization has not yet completed,
+ *    see the explanation below.
+ * 2. Skipping poisoning is requested via FPI_SKIP_KASAN_POISON,
+ *    see the comment next to it.
+ * 3. Skipping poisoning is requested via __GFP_SKIP_KASAN_POISON,
+ *    see the comment next to it.
+ *
+ * Poisoning pages during deferred memory init will greatly lengthen the
+ * process and cause problem in large memory systems as the deferred pages
+ * initialization is done with interrupt disabled.
+ *
+ * Assuming that there will be no reference to those newly initialized
+ * pages before they are ever allocated, this should have no effect on
+ * KASAN memory tracking as the poison will be properly inserted at page
+ * allocation time. The only corner case is when pages are allocated by
+ * on-demand allocation and then freed again before the deferred pages
+ * initialization is done, but this is not likely to happen.
+ */
+static inline bool should_skip_kasan_poison(struct page *page, fpi_t fpi_flags)
+{
+	return deferred_pages_enabled() ||
+	       (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+		(fpi_flags & FPI_SKIP_KASAN_POISON)) ||
+	       PageSkipKASanPoison(page);
+}
+
 static void kernel_init_free_pages(struct page *page, int numpages, bool zero_tags)
 {
 	int i;
-- 
2.25.1