linux-kernel - [PATCH v2 2/9] arm64: hugetlbpages: Support handling swap entries in huge_pte

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Date:   Wed,  5 Apr 2017 14:37:15 +0100
From:   Punit Agrawal <punit.agrawal@....com>
To:     catalin.marinas@....com, will.deacon@....com,
        akpm@...ux-foundation.org, mark.rutland@....com
Cc:     Punit Agrawal <punit.agrawal@....com>, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        tbaicar@...eaurora.org, kirill.shutemov@...ux.intel.com,
        mike.kravetz@...cle.com, hillf.zj@...baba-inc.com,
        steve.capper@....com, David Woods <dwoods@...lanox.com>
Subject: [PATCH v2 2/9] arm64: hugetlbpages: Support handling swap entries in huge_pte_offset()

huge_pte_offset() does not correctly handle poisoned or migration page
table entries. It returns NULL instead of the offset when it encounters
a swap entry. This leads to errors such as

[  344.165544] mm/pgtable-generic.c:33: bad pmd 000000083af00074.

in the kernel log when unmapping memory on process exit.

huge_pte_offset() is now provided with the size of the hugepage being
accessed. Use the size to find the correct page table entry to return.

Signed-off-by: Punit Agrawal <punit.agrawal@....com>
Cc: David Woods <dwoods@...lanox.com>
---
 arch/arm64/mm/hugetlbpage.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 1bc08ae49e6a..009648c4500f 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -194,36 +194,36 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
 {
 	pgd_t *pgd;
 	pud_t *pud;
-	pmd_t *pmd = NULL;
-	pte_t *pte = NULL;
+	pmd_t *pmd;
+	pte_t *pte;
 
 	pgd = pgd_offset(mm, addr);
 	pr_debug("%s: addr:0x%lx pgd:%p\n", __func__, addr, pgd);
 	if (!pgd_present(*pgd))
 		return NULL;
+
 	pud = pud_offset(pgd, addr);
-	if (!pud_present(*pud))
+	if (pud_none(*pud) && sz != PUD_SIZE)
 		return NULL;
-
-	if (pud_huge(*pud))
+	else if (!pud_table(*pud))
 		return (pte_t *)pud;
+
+	if (sz == CONT_PMD_SIZE)
+		addr &= CONT_PMD_MASK;
+
 	pmd = pmd_offset(pud, addr);
-	if (!pmd_present(*pmd))
+	if (pmd_none(*pmd) &&
+	    !(sz == PMD_SIZE || sz == CONT_PMD_SIZE))
 		return NULL;
-
-	if (pte_cont(pmd_pte(*pmd))) {
-		pmd = pmd_offset(
-			pud, (addr & CONT_PMD_MASK));
-		return (pte_t *)pmd;
-	}
-	if (pmd_huge(*pmd))
+	else if (!pmd_table(*pmd))
 		return (pte_t *)pmd;
-	pte = pte_offset_kernel(pmd, addr);
-	if (pte_present(*pte) && pte_cont(*pte)) {
+
+	if (sz == CONT_PTE_SIZE) {
 		pte = pte_offset_kernel(
 			pmd, (addr & CONT_PTE_MASK));
 		return pte;
 	}
+
 	return NULL;
 }
 
-- 
2.11.0