linux-kernel - [tip:x86/mm] x86/KASLR: Update KERNEL_IMAGE

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Date:   Sat, 6 Oct 2018 06:06:53 -0700
From:   tip-bot for Baoquan He <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, luto@...nel.org, dvlasenk@...hat.com,
        tglx@...utronix.de, bhe@...hat.com, luto@...capital.net,
        torvalds@...ux-foundation.org, bp@...en8.de, hpa@...or.com,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        dave.hansen@...ux.intel.com, brgerst@...il.com, riel@...riel.com
Subject: [tip:x86/mm] x86/KASLR: Update KERNEL_IMAGE_SIZE description

Commit-ID:  06d4a462e954756f3d3d54e6f3f1bdc2e6f592a9
Gitweb:     https://git.kernel.org/tip/06d4a462e954756f3d3d54e6f3f1bdc2e6f592a9
Author:     Baoquan He <bhe@...hat.com>
AuthorDate: Sat, 6 Oct 2018 16:43:25 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sat, 6 Oct 2018 14:46:46 +0200

x86/KASLR: Update KERNEL_IMAGE_SIZE description

Currently CONFIG_RANDOMIZE_BASE=y is set by default, which makes some of the
old comments above the KERNEL_IMAGE_SIZE definition out of date. Update them
to the current state of affairs.

Signed-off-by: Baoquan He <bhe@...hat.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: corbet@....net
Cc: linux-doc@...r.kernel.org
Cc: thgarnie@...gle.com
Link: http://lkml.kernel.org/r/20181006084327.27467-2-bhe@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/page_64_types.h | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index 6afac386a434..cd0cf1c568b4 100644
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -59,13 +59,16 @@
 #endif
 
 /*
- * Kernel image size is limited to 1GiB due to the fixmap living in the
- * next 1GiB (see level2_kernel_pgt in arch/x86/kernel/head_64.S). Use
- * 512MiB by default, leaving 1.5GiB for modules once the page tables
- * are fully set up. If kernel ASLR is configured, it can extend the
- * kernel page table mapping, reducing the size of the modules area.
+ * Maximum kernel image size is limited to 1 GiB, due to the fixmap living
+ * in the next 1 GiB (see level2_kernel_pgt in arch/x86/kernel/head_64.S).
+ *
+ * On KASLR use 1 GiB by default, leaving 1 GiB for modules once the
+ * page tables are fully set up.
+ *
+ * If KASLR is disabled we can shrink it to 0.5 GiB and increase the size
+ * of the modules area to 1.5 GiB.
  */
-#if defined(CONFIG_RANDOMIZE_BASE)
+#ifdef CONFIG_RANDOMIZE_BASE
 #define KERNEL_IMAGE_SIZE	(1024 * 1024 * 1024)
 #else
 #define KERNEL_IMAGE_SIZE	(512 * 1024 * 1024)