powerpc/mm: Return NULL for not present hugetlb page

We need to check whether pte is present in follow_huge_addr() and
properly return NULL if mapping is not present. Also use READ_ONCE
when dereferencing pte_t address.

Without this patch, we may wrongly return a zero pfn page in
follow_huge_addr().

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 0ce968b00b7c665967ca3addc26d0cc04a72f729..3385e3d0506ec575f3eeebad77d2c65264a3acf3 100644 (file)
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -689,27 +689,34 @@ void hugetlb_free_pgd_range(struct mmu_gather *tlb,
 struct page *
 follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
 {
-       pte_t *ptep;
-       struct page *page;
+       pte_t *ptep, pte;
        unsigned shift;
        unsigned long mask, flags;
+       struct page *page = ERR_PTR(-EINVAL);
+
+       local_irq_save(flags);
+       ptep = find_linux_pte_or_hugepte(mm->pgd, address, &shift);
+       if (!ptep)
+               goto no_page;
+       pte = READ_ONCE(*ptep);
        /*
+        * Verify it is a huge page else bail.
         * Transparent hugepages are handled by generic code. We can skip them
         * here.
         */
-       local_irq_save(flags);
-       ptep = find_linux_pte_or_hugepte(mm->pgd, address, &shift);
+       if (!shift || pmd_trans_huge(__pmd(pte_val(pte))))
+               goto no_page;
 
-       /* Verify it is a huge page else bail. */
-       if (!ptep || !shift || pmd_trans_huge(*(pmd_t *)ptep)) {
-               local_irq_restore(flags);
-               return ERR_PTR(-EINVAL);
+       if (!pte_present(pte)) {
+               page = NULL;
+               goto no_page;
        }
        mask = (1UL << shift) - 1;
-       page = pte_page(*ptep);
+       page = pte_page(pte);
        if (page)
                page += (address & mask) / PAGE_SIZE;
 
+no_page:
        local_irq_restore(flags);
        return page;
 }