Revert "kmsan: unpoison @tlb in arch_tlb_gather_mmu()"

This reverts commit ac801e7e.

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.

Link: https://lkml.kernel.org/r/20221110113541.1844156-1-glider@google.comSigned-off-by: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmu_gather.c

 #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>
@@ -299,15 +298,6 @@ 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;