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x86-64: add comment for RODATA large page retainment

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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>
This commit is contained in:
Suresh Siddha 2009-10-19 06:12:04 -07:00 committed by H. Peter Anvin
parent 74e081797b
commit d6cc1c3af7
1 changed files with 12 additions and 1 deletions
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13
arch/x86/kernel/vmlinux.lds.S
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@ -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 \