linux-kernel - [PATCH] mm: make 'highmem' symbol ro_after

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Message-Id: <20220124170555.1054480-1-ardb@kernel.org>
Date:   Mon, 24 Jan 2022 18:05:55 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH] mm: make 'highmem' symbol ro_after_init

The 'highmem' variable is only set at boot, so we can make it
ro_after_init and prevent it from being corrupted inadvertently, or from
ending up in a contended cacheline.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 mm/memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index c125c4969913..50e82cb94ccc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -106,7 +106,7 @@ EXPORT_SYMBOL(mem_map);
  * highstart_pfn must be the same; there must be no gap between ZONE_NORMAL
  * and ZONE_HIGHMEM.
  */
-void *high_memory;
+void *high_memory __ro_after_init;
 EXPORT_SYMBOL(high_memory);
 
 /*
-- 
2.30.2