lkml.org 
[lkml]   [2022]   [Mar]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
Subject[PATCH v2 22/48] kmsan: unpoison @tlb in arch_tlb_gather_mmu()
From
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@google.com>
---
Link: https://linux-review.googlesource.com/id/I76abee411b8323acfdbc29bc3a60dca8cff2de77
---
mm/mmu_gather.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index afb7185ffdc45..2f3821268b311 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/mm_inline.h>
@@ -253,6 +254,15 @@ void tlb_flush_mmu(struct mmu_gather *tlb)
static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
bool fullmm)
{
+ /*
+ * 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_memory(tlb, sizeof(*tlb));
tlb->mm = mm;
tlb->fullmm = fullmm;

--
2.35.1.1021.g381101b075-goog
\
 
 \ /
  Last update: 2022-03-29 14:44    [W:0.296 / U:0.504 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site