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authorSuresh Siddha <suresh.b.siddha@intel.com>2009-10-19 06:12:04 -0700
committerH. Peter Anvin <hpa@zytor.com>2009-10-20 14:46:01 +0900
commitd6cc1c3af760c1d3f6b42f6e52b08718a6207cf1 (patch)
treef7124eeb8725775c94f7e5d07a5ab1c3c3c8bbb4 /arch/x86
parent74e081797bd9d2a7d8005fe519e719df343a2ba8 (diff)
x86-64: add comment for RODATA large page retainment
Add a comment explaining why RODATA is aligned to 2 MB. Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kernel/vmlinux.lds.S13
1 files changed, 12 insertions, 1 deletions
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 14763790e41..fd2dabec1df 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -42,7 +42,18 @@ jiffies_64 = jiffies;
#endif
#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
-
+/*
+ * On 64-bit, align RODATA to 2MB so that even with CONFIG_DEBUG_RODATA
+ * we retain large page mappings for boundaries spanning kernel text, rodata
+ * and data sections.
+ *
+ * However, kernel identity mappings will have different RWX permissions
+ * to the pages mapping to text and to the pages padding (which are freed) the
+ * text section. Hence kernel identity mappings will be broken to smaller
+ * pages. For 64-bit, kernel text and kernel identity mappings are different,
+ * so we can enable protection checks that come with CONFIG_DEBUG_RODATA,
+ * as well as retain 2MB large page mappings for kernel text.
+ */
#define X64_ALIGN_DEBUG_RODATA_BEGIN . = ALIGN(HPAGE_SIZE);
#define X64_ALIGN_DEBUG_RODATA_END \