[PATCH RFC 07/20] kasan: introduce kasan_mempool_unpoison_pages

[andrey.konovalov@linux.dev]

From: Andrey Konovalov <andreyknvl@google.com>

Introduce and document a new kasan_mempool_unpoison_pages hook to be used
by the mempool code instead of kasan_unpoison_pages.

This hook is not functionally different from kasan_unpoison_pages, but
using it improves the mempool code readability.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 include/linux/kasan.h | 25 +++++++++++++++++++++++++
 mm/kasan/common.c     |  6 ++++++
 2 files changed, 31 insertions(+)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index de2a695ad34d..f8ebde384bd7 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -225,6 +225,9 @@ bool __kasan_mempool_poison_pages(struct page *page, unsigned int order,
  * This function is similar to kasan_mempool_poison_object() but operates on
  * page allocations.
  *
+ * Before the poisoned allocation can be reused, it must be unpoisoned via
+ * kasan_mempool_unpoison_pages().
+ *
  * Return: true if the allocation can be safely reused; false otherwise.
  */
 static __always_inline bool kasan_mempool_poison_pages(struct page *page,
@@ -235,6 +238,27 @@ static __always_inline bool kasan_mempool_poison_pages(struct page *page,
 	return true;
 }
 
+void __kasan_mempool_unpoison_pages(struct page *page, unsigned int order,
+				    unsigned long ip);
+/**
+ * kasan_mempool_unpoison_pages - Unpoison a mempool page allocation.
+ * @page: Pointer to the page allocation.
+ * @order: Order of the allocation.
+ *
+ * This function is intended for kernel subsystems that cache page allocations
+ * to reuse them instead of freeing them back to page_alloc (e.g. mempool).
+ *
+ * This function unpoisons a page allocation that was previously poisoned by
+ * kasan_mempool_poison_pages() without zeroing the allocation's memory. For
+ * the tag-based modes, this function assigns a new tag to the allocation.
+ */
+static __always_inline void kasan_mempool_unpoison_pages(struct page *page,
+							 unsigned int order)
+{
+	if (kasan_enabled())
+		__kasan_mempool_unpoison_pages(page, order, _RET_IP_);
+}
+
 bool __kasan_mempool_poison_object(void *ptr, unsigned long ip);
 /**
  * kasan_mempool_poison_object - Check and poison a mempool slab allocation.
@@ -353,6 +377,7 @@ static inline bool kasan_mempool_poison_pages(struct page *page, unsigned int or
 {
 	return true;
 }
+static inline void kasan_mempool_unpoison_pages(struct page *page, unsigned int order) {}
 static inline bool kasan_mempool_poison_object(void *ptr)
 {
 	return true;
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 9ccc78b20cf2..6283f0206ef6 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -439,6 +439,12 @@ bool __kasan_mempool_poison_pages(struct page *page, unsigned int order,
 	return true;
 }
 
+void __kasan_mempool_unpoison_pages(struct page *page, unsigned int order,
+				    unsigned long ip)
+{
+	__kasan_unpoison_pages(page, order, false);
+}
+
 bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
 {
 	struct folio *folio;
-- 
2.25.1