From d6cc1c3af760c1d3f6b42f6e52b08718a6207cf1 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Mon, 19 Oct 2009 06:12:04 -0700 Subject: [PATCH] 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 Signed-off-by: H. Peter Anvin --- arch/x86/kernel/vmlinux.lds.S | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 14763790e415..fd2dabec1dff 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 \ -- 2.34.1