[Patch v2] x86/head/64: remove redundant check on level2_kernel_pgt's _PAGE_PRESENT bit

[Wei Yang]

This patch tries to remove a redundant check on kernel code's PMD
_PAGE_PRESENT attribute before fix up.

Current process looks like this:

    pmd in [0, _text)
        unset _PAGE_PRESENT
    pmd in [_text, _end]
        if (_PAGE_PRESENT)
            fix up delta
    pmd in (_end, 512)
        unset _PAGE_PRESENT

Since we have compiled in _PAGE_PRESENT in this page table, it is not
necessary to check _PAGE_PRESENT again before fixing up delta

Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Steve Wahl <steve.wahl@xxxxxxx>

---
v2: adjust the change log to emphasize the redundant check
---
 arch/x86/kernel/head64.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index a817ed0724d1..bac33ec19aa2 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -260,8 +260,7 @@ unsigned long __head __startup_64(unsigned long physaddr,
 
 	/* fixup pages that are part of the kernel image */
 	for (; i <= pmd_index((unsigned long)_end); i++)
-		if (pmd[i] & _PAGE_PRESENT)
-			pmd[i] += load_delta;
+		pmd[i] += load_delta;
 
 	/* invalidate pages after the kernel image */
 	for (; i < PTRS_PER_PMD; i++)
-- 
2.34.1