ARM: mm: Allow an empty PMD in alloc_init_pte()

The Android patch titled "ARM: allow the kernel text section to
be made read-only" modifies alloc_init_pte() and adds a BUG_ON
to detect the case where a section mapping is being overwritten.
However the test doesn't allow for the legitimate case where the
PMD is empty, as can happen for kernels built with CONFIG_ARM_LPAE.
So extend the test to allow this.

Change-Id: I28eeaefd856bae63a5532980e41e0fd4d8922e79
Signed-off-by: Jon Medhurst <tixy@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index cc9c66694f342bea481a56d7ee5803799e6c4fc6..394342d0482e0f14f75e15558b12aa6e38a23ff1 100644 (file)
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -627,7 +627,7 @@ static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr,
        pte_t *pte = start_pte + pte_index(addr);
 
        /* If replacing a section mapping, the whole section must be replaced */
-       BUG_ON(pmd_bad(*pmd) && ((addr | end) & ~PMD_MASK));
+       BUG_ON(!pmd_none(*pmd) && pmd_bad(*pmd) && ((addr | end) & ~PMD_MASK));
 
        do {
                set_pte_ext(pte, pfn_pte(pfn, __pgprot(type->prot_pte)), 0);