linux-kernel - [PATCH 5/4] x86/mm: Further simplify 1 GB kernel linear mappings handling

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Message-ID: <20150305072313.GA23951@gmail.com>
Date:	Thu, 5 Mar 2015 08:23:14 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
	tony@...mide.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, jgross@...e.com, luto@...capital.net,
	toshi.kani@...com, dave.hansen@...ux.intel.com, JBeulich@...e.com,
	pavel@....cz, qiuxishi@...wei.com, david.vrabel@...rix.com,
	bp@...e.de, vbabka@...e.cz, iamjoonsoo.kim@....com,
	decui@...rosoft.com, linux-kernel@...r.kernel.org, x86@...nel.org,
	julia.lawall@...6.fr, "Luis R. Rodriguez" <mcgrof@...e.com>
Subject: [PATCH 5/4] x86/mm: Further simplify 1 GB kernel linear mappings
 handling


It's a bit pointless to allow Kconfig configuration for 1GB kernel
mappings, it's already hidden behind a 'default y' and CONFIG_EXPERT.

Remove this complication and simplify the code by renaming
CONFIG_ENABLE_DIRECT_GBPAGES to CONFIG_X86_DIRECT_GBPAGES and
document the DEBUG_PAGE_ALLOC and KMEMCHECK quirks.

Cc: Luis R. Rodriguez <mcgrof@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Borislav Petkov <bp@...e.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: David Vrabel <david.vrabel@...rix.com>
Cc: Dexuan Cui <decui@...rosoft.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: JBeulich@...e.com
Cc: Jan Beulich <JBeulich@...e.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Pavel Machek <pavel@....cz>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tony Lindgren <tony@...mide.com>
Cc: Toshi Kani <toshi.kani@...com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Xishi Qiu <qiuxishi@...wei.com>
Cc: julia.lawall@...6.fr
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/Kconfig   | 23 +++++++----------------
 arch/x86/mm/init.c |  7 +------
 2 files changed, 8 insertions(+), 22 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4d06e1c8294a..54d528a37ff4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1299,22 +1299,13 @@ config ARCH_DMA_ADDR_T_64BIT
 	def_bool y
 	depends on X86_64 || HIGHMEM64G
 
-config ENABLE_DIRECT_GBPAGES
-	def_bool y
-	depends on X86_64 && !DEBUG_PAGEALLOC && !KMEMCHECK
-
-config DIRECT_GBPAGES
-	bool "Enable 1GB pages for kernel pagetables" if EXPERT
-	default y
-	depends on ENABLE_DIRECT_GBPAGES
-	---help---
-	  Enable by default the kernel linear mapping to use 1GB pages on CPUs
-	  that support it. This can improve the kernel's performance a tiny bit
-	  by reducing TLB pressure. If in doubt, say "Y". If you've disabled
-	  option but your platform is capable of handling support for this
-	  you can use the gbpages kernel parameter. Likewise if you've enabled
-	  this but you'd like to force disable this option you can use the
-	  nogbpages kernel parameter.
+config X86_DIRECT_GBPAGES
+	def_bool (X86_64 && !DEBUG_PAGEALLOC && !KMEMCHECK)
+	---help---
+	  Certain kernel features effectively disable kernel
+	  linear 1 GB mappings (even if the CPU otherwise
+	  supports them), so don't confuse the user by printing
+	  that we have them enabled.
 
 # Common NUMA Features
 config NUMA
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index c35ba8bce7cb..8704153f2675 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -133,15 +133,10 @@ int after_bootmem;
 
 static int page_size_mask;
 
-early_param_on_off("gbpages", "nogbpages",
-		   direct_gbpages, CONFIG_DIRECT_GBPAGES);
+early_param_on_off("gbpages", "nogbpages", direct_gbpages, CONFIG_X86_DIRECT_GBPAGES);
 
 static void __init init_gbpages(void)
 {
-	if (!IS_ENABLED(CONFIG_ENABLE_DIRECT_GBPAGES)) {
-		direct_gbpages = 0;
-		return;
-	}
 	if (direct_gbpages && cpu_has_gbpages) {
 		printk(KERN_INFO "Using GB pages for direct mapping\n");
 		page_size_mask |= 1 << PG_LEVEL_1G;
--
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