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Commit 7b868e81 authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Michael Ellerman
Browse files

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: default avatarDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 13bd817b

arch/powerpc/mm/hugetlbpage.c

+16 −9
Original line number Diff line number Diff line
@@ -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;

}