When walking the page tables to resolve an address that points to
!p*d_present() entry, huge_pte_offset() returns inconsistent values
depending on the level of page table (PUD or PMD).
It returns NULL in the case of a PUD entry while in the case of a PMD
entry, it returns a pointer to the page table entry.
A similar inconsitency exists when handling swap entries - returns NULL
for a PUD entry while a pointer to the pte_t is retured for the PMD
entry.
Update huge_pte_offset() to make the behaviour consistent - return NULL
in the case of p*d_none() and a pointer to the pte_t for hugepage or
swap entries.
Document the behaviour to clarify the expected behaviour of this
function. This is to set clear semantics for architecture specific
implementations of huge_pte_offset().
Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
---
mm/hugetlb.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index bc48ee783dd9..72dd1139a8e4 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4603,6 +4603,13 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
return pte;
}
+/*
+ * huge_pte_offset() - Walk the page table to resolve the hugepage
+ * entry at address @addr
+ *
+ * Return: Pointer to page table or swap entry (PUD or PMD) for address @addr
+ * or NULL if the entry is p*d_none().
+ */
pte_t *huge_pte_offset(struct mm_struct *mm,
unsigned long addr, unsigned long sz)
{
@@ -4617,13 +4624,22 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
p4d = p4d_offset(pgd, addr);
if (!p4d_present(*p4d))
return NULL;
+
pud = pud_offset(p4d, addr);
- if (!pud_present(*pud))
+ if (pud_none(*pud))
return NULL;
- if (pud_huge(*pud))
+ /* hugepage or swap? */
+ if (pud_huge(*pud) || !pud_present(*pud))
return (pte_t *)pud;
+
pmd = pmd_offset(pud, addr);
- return (pte_t *) pmd;
+ if (pmd_none(*pmd))
+ return NULL;
+ /* hugepage or swap? */
+ if (pmd_huge(*pmd) || !pmd_present(*pmd))
+ return (pte_t *) pmd;
+
+ return NULL;
}
#endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
--
2.11.0
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