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Subject[PATCH mm v3 27/38] kasan, page_alloc: allow skipping unpoisoning for HW_TAGS
Date
From: Andrey Konovalov <andreyknvl@google.com>

Add a new GFP flag __GFP_SKIP_KASAN_UNPOISON that allows skipping KASAN
poisoning for page_alloc allocations. The flag is only effective with
HW_TAGS KASAN.

This flag will be used by vmalloc code for page_alloc allocations
backing vmalloc() mappings in a following patch. The reason to skip
KASAN poisoning for these pages in page_alloc is because vmalloc code
will be poisoning them instead.

Also reword the comment for __GFP_SKIP_KASAN_POISON.

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

---

Changes v2->v3:
- Update patch description.
---
include/linux/gfp.h | 18 +++++++++++-------
mm/page_alloc.c | 24 +++++++++++++++++-------
2 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 42b845cdc131..6781f84345d1 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -54,9 +54,10 @@ struct vm_area_struct;
#define ___GFP_THISNODE 0x200000u
#define ___GFP_ACCOUNT 0x400000u
#define ___GFP_ZEROTAGS 0x800000u
-#define ___GFP_SKIP_KASAN_POISON 0x1000000u
+#define ___GFP_SKIP_KASAN_UNPOISON 0x1000000u
+#define ___GFP_SKIP_KASAN_POISON 0x2000000u
#ifdef CONFIG_LOCKDEP
-#define ___GFP_NOLOCKDEP 0x2000000u
+#define ___GFP_NOLOCKDEP 0x4000000u
#else
#define ___GFP_NOLOCKDEP 0
#endif
@@ -231,21 +232,24 @@ struct vm_area_struct;
* %__GFP_ZEROTAGS zeroes memory tags at allocation time if the memory itself
* is being zeroed (either via __GFP_ZERO or via init_on_alloc).
*
- * %__GFP_SKIP_KASAN_POISON returns a page which does not need to be poisoned
- * on deallocation. Typically used for userspace pages. Currently only has an
- * effect in HW tags mode.
+ * %__GFP_SKIP_KASAN_UNPOISON makes KASAN skip unpoisoning on page allocation.
+ * Only effective in HW_TAGS mode.
+ *
+ * %__GFP_SKIP_KASAN_POISON makes KASAN skip poisoning on page deallocation.
+ * Typically, used for userspace pages. Only effective in HW_TAGS mode.
*/
#define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN)
#define __GFP_COMP ((__force gfp_t)___GFP_COMP)
#define __GFP_ZERO ((__force gfp_t)___GFP_ZERO)
#define __GFP_ZEROTAGS ((__force gfp_t)___GFP_ZEROTAGS)
-#define __GFP_SKIP_KASAN_POISON ((__force gfp_t)___GFP_SKIP_KASAN_POISON)
+#define __GFP_SKIP_KASAN_UNPOISON ((__force gfp_t)___GFP_SKIP_KASAN_UNPOISON)
+#define __GFP_SKIP_KASAN_POISON ((__force gfp_t)___GFP_SKIP_KASAN_POISON)

/* Disable lockdep for GFP context tracking */
#define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)

/* Room for N __GFP_FOO bits */
-#define __GFP_BITS_SHIFT (25 + IS_ENABLED(CONFIG_LOCKDEP))
+#define __GFP_BITS_SHIFT (26 + IS_ENABLED(CONFIG_LOCKDEP))
#define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))

/**
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 497db24ed169..f1d5b80591c4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2394,6 +2394,21 @@ static bool check_new_pages(struct page *page, unsigned int order)
return false;
}

+static inline bool should_skip_kasan_unpoison(gfp_t flags, bool init_tags)
+{
+ /* Don't skip if a software KASAN mode is enabled. */
+ if (!IS_ENABLED(CONFIG_KASAN_HW_TAGS))
+ return false;
+
+ /*
+ * For hardware tag-based KASAN, skip if either:
+ *
+ * 1. Memory tags have already been cleared via tag_clear_highpage().
+ * 2. Skipping has been requested via __GFP_SKIP_KASAN_UNPOISON.
+ */
+ return init_tags || (flags & __GFP_SKIP_KASAN_UNPOISON);
+}
+
inline void post_alloc_hook(struct page *page, unsigned int order,
gfp_t gfp_flags)
{
@@ -2433,13 +2448,8 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
/* Note that memory is already initialized by the loop above. */
init = false;
}
- /*
- * If either a software KASAN mode is enabled, or,
- * in the case of hardware tag-based KASAN,
- * if memory tags have not been cleared via tag_clear_highpage().
- */
- if (!IS_ENABLED(CONFIG_KASAN_HW_TAGS) || !init_tags) {
- /* Mark shadow memory or set memory tags. */
+ if (!should_skip_kasan_unpoison(gfp_flags, init_tags)) {
+ /* Unpoison shadow memory or set memory tags. */
kasan_unpoison_pages(page, order, init);

/* Note that memory is already initialized by KASAN. */
--
2.25.1
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