diff options
| author | Suresh Siddha <suresh.b.siddha@intel.com> | 2009-10-19 06:12:04 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2009-10-20 14:46:01 +0900 |
| commit | d6cc1c3af760c1d3f6b42f6e52b08718a6207cf1 (patch) | |
| tree | f7124eeb8725775c94f7e5d07a5ab1c3c3c8bbb4 | |
| parent | 74e081797bd9d2a7d8005fe519e719df343a2ba8 (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>
| -rw-r--r-- | arch/x86/kernel/vmlinux.lds.S | 13 |
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 \ |