This is a hack to reduce stackdepot pressure.
struct mmu_gather contains 7 1-bit fields packed into a 32-bit unsigned
int value. The remaining 25 bits remain uninitialized and are never used,
but KMSAN updates the origin for them in zap_pXX_range() in mm/memory.c,
thus creating very long origin chains. This is technically correct, but
consumes too much memory.
Unpoisoning the whole structure will prevent creating such chains.
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
To: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
---
v4:
- removed a TODO, updated patch description
Change-Id: I22a201e7e4f67ed74f8129072f12e5351b26103a
---
mm/mmu_gather.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index a3538cb2bcbee..d3d57c276e301 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -1,6 +1,7 @@
#include <linux/gfp.h>
#include <linux/highmem.h>
#include <linux/kernel.h>
+#include <linux/kmsan-checks.h>
#include <linux/mmdebug.h>
#include <linux/mm_types.h>
#include <linux/pagemap.h>
@@ -264,6 +265,15 @@ void tlb_flush_mmu(struct mmu_gather *tlb)
void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
unsigned long start, unsigned long end)
{
+ /*
+ * struct mmu_gather contains 7 1-bit fields packed into a 32-bit
+ * unsigned int value. The remaining 25 bits remain uninitialized
+ * and are never used, but KMSAN updates the origin for them in
+ * zap_pXX_range() in mm/memory.c, thus creating very long origin
+ * chains. This is technically correct, but consumes too much memory.
+ * Unpoisoning the whole structure will prevent creating such chains.
+ */
+ kmsan_unpoison_shadow(tlb, sizeof(*tlb));
tlb->mm = mm;
/* Is it from 0 to ~0? */
--
2.25.1.696.g5e7596f4ac-goog
