[PATCH v6 01/39] kasan, page_alloc: deduplicate should_skip_kasan_poison

andrey.konovalov
2022-01-24T18:32:52Z

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 3589febc6d31..25d4f9ad3525 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -378,25 +378,9 @@ 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 */
@@ -447,11 +431,9 @@ 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)
@@ -1271,6 +1253,35 @@ 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;