From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 9D88F6B02F4 for ; Tue, 25 Jul 2017 11:41:36 -0400 (EDT) Received: by mail-pg0-f69.google.com with SMTP id b8so47484864pgn.10 for ; Tue, 25 Jul 2017 08:41:36 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id b5si437857pgc.359.2017.07.25.08.41.35 for ; Tue, 25 Jul 2017 08:41:35 -0700 (PDT) From: Punit Agrawal Subject: [PATCH 1/1] mm/hugetlb: Make huge_pte_offset() consistent and document behaviour Date: Tue, 25 Jul 2017 16:41:14 +0100 Message-Id: <20170725154114.24131-2-punit.agrawal@arm.com> In-Reply-To: <20170725154114.24131-1-punit.agrawal@arm.com> References: <20170725154114.24131-1-punit.agrawal@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Punit Agrawal , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, steve.capper@arm.com, will.deacon@arm.com, catalin.marinas@arm.com, kirill.shutemov@linux.intel.com, Michal Hocko , Mike Kravetz 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 --- 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org