linux-kernel - [patch V4 1/8] mm/highmem: Provide and use CONFIG_DEBUG_KMAP

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Message-Id: <20201118204006.869487226@linutronix.de>
Date:   Wed, 18 Nov 2020 20:48:39 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Linus Torvalds <torvalds@...uxfoundation.org>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: [patch V4 1/8] mm/highmem: Provide and use CONFIG_DEBUG_KMAP_LOCAL

CONFIG_KMAP_LOCAL can be enabled by x86/32bit even if CONFIG_HIGHMEM is not
enabled for temporary MMIO space mappings.

Provide it as a seperate config option which depends on CONFIG_KMAP_LOCAL
and let CONFIG_DEBUG_HIGHMEM select it.

This won't increase the debug coverage of this significantly but it paves
the way to do so.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
V4: New patch
---
 include/asm-generic/kmap_size.h |    2 +-
 lib/Kconfig.debug               |    8 ++++++++
 mm/highmem.c                    |    4 ++--
 3 files changed, 11 insertions(+), 3 deletions(-)

--- a/include/asm-generic/kmap_size.h
+++ b/include/asm-generic/kmap_size.h
@@ -3,7 +3,7 @@
 #define _ASM_GENERIC_KMAP_SIZE_H
 
 /* For debug this provides guard pages between the maps */
-#ifdef CONFIG_DEBUG_HIGHMEM
+#ifdef CONFIG_DEBUG_KMAP_LOCAL
 # define KM_MAX_IDX	33
 #else
 # define KM_MAX_IDX	16
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -849,9 +849,17 @@ config DEBUG_PER_CPU_MAPS
 
 	  Say N if unsure.
 
+config DEBUG_KMAP_LOCAL
+	bool "Debug kmap_local temporary mappings"
+	depends on DEBUG_KERNEL && KMAP_LOCAL
+	help
+	  This option enables additional error checking for the kmap_local
+	  infrastructure.  Disable for production use.
+
 config DEBUG_HIGHMEM
 	bool "Highmem debugging"
 	depends on DEBUG_KERNEL && HIGHMEM
+	select DEBUG_KMAP_LOCAL
 	help
 	  This option enables additional error checking for high memory
 	  systems.  Disable for production systems.
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -368,10 +368,10 @@ EXPORT_SYMBOL(kunmap_high);
 static DEFINE_PER_CPU(int, __kmap_local_idx);
 
 /*
- * With DEBUG_HIGHMEM the stack depth is doubled and every second
+ * With DEBUG_KMAP_LOCAL the stack depth is doubled and every second
  * slot is unused which acts as a guard page
  */
-#ifdef CONFIG_DEBUG_HIGHMEM
+#ifdef CONFIG_DEBUG_KMAP_LOCAL
 # define KM_INCR	2
 #else
 # define KM_INCR	1