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powerpc/mm: Return NULL for not present hugetlb page

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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>
This commit is contained in:
Aneesh Kumar K.V 2015-05-11 11:58:29 +05:30 committed by Michael Ellerman
parent 13bd817bb8
commit 7b868e81be
1 changed files with 16 additions and 9 deletions
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25
arch/powerpc/mm/hugetlbpage.c
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@ -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;
}