linux-kernel - [PATCH] Revert "kmsan: unpoison @tlb in arch_tlb_gather

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Date:   Thu, 10 Nov 2022 12:35:41 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     glider@...gle.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Marco Elver <elver@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>
Subject: [PATCH] Revert "kmsan: unpoison @tlb in arch_tlb_gather_mmu()"

This reverts commit ac801e7e252c5588325e3c983c7d4167fc68c024.

The patch in question was picked to -mm from the KMSAN v6 patch series
(https://lore.kernel.org/linux-mm/20220905122452.2258262-1-glider@google.com/)
and sneaked into mainline despite its removal from the v7 series
(https://lore.kernel.org/linux-mm/20220915150417.722975-1-glider@google.com/)

Currently KMSAN does not warn about origin chains hitting the maximum
depth, so keeping @tlb poisoned won't result in any inconveniences.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Eric Biggers <ebiggers@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Marco Elver <elver@...gle.com>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Will Deacon <will@...nel.org>
Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
 mm/mmu_gather.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index add4244e5790d..a71924bd38c0d 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -1,7 +1,6 @@
 #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>
@@ -266,15 +265,6 @@ 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;
 
-- 
2.38.1.431.g37b22c650d-goog