From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id C958B6B025F for ; Tue, 25 Jul 2017 10:38:01 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id v68so158562876pfi.13 for ; Tue, 25 Jul 2017 07:38:01 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id e126si8117551pfh.616.2017.07.25.07.38.00 for ; Tue, 25 Jul 2017 07:38:00 -0700 (PDT) From: Punit Agrawal Subject: Re: [RFC PATCH 1/2] mm/hugetlb: Make huge_pte_offset() consistent between PUD and PMD entries References: <20170724173318.966-1-punit.agrawal@arm.com> <20170724173318.966-2-punit.agrawal@arm.com> <20170725122907.bvmubwcfmqalp6r3@localhost> Date: Tue, 25 Jul 2017 15:37:57 +0100 In-Reply-To: <20170725122907.bvmubwcfmqalp6r3@localhost> (Catalin Marinas's message of "Tue, 25 Jul 2017 13:29:07 +0100") Message-ID: <87k22wk2ey.fsf@e105922-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: Catalin Marinas Cc: Andrew Morton , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, steve.capper@arm.com, will.deacon@arm.com, kirill.shutemov@linux.intel.com, Michal Hocko , Mike Kravetz Catalin Marinas writes: > Hi Punit, > > On Mon, Jul 24, 2017 at 06:33:17PM +0100, Punit Agrawal wrote: >> When walking the page tables to resolve an address that points to >> !present_p*d() entry, huge_pte_offset() returns inconsistent values >> depending on the level of page table (PUD or PMD). >> >> In the case of a PUD entry, it returns NULL while in the case of a PMD >> entry, it returns a pointer to the page table entry. >> >> Make huge_pte_offset() consistent by always returning NULL on >> encountering a !present_p*d() entry. Document the behaviour to clarify >> the expected semantics of this function. > > Nitpick: "p*d_present" instead of "present_p*d". Thanks for spotting. Fixed both the instances locally. > >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index bc48ee783dd9..686eb6fa9eb1 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 entry (PUD or PMD) for address @addr >> + * or NULL if the entry is not present. >> + */ >> pte_t *huge_pte_offset(struct mm_struct *mm, >> unsigned long addr, unsigned long sz) >> { >> @@ -4617,13 +4624,20 @@ 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)) >> return NULL; >> if (pud_huge(*pud)) >> return (pte_t *)pud; >> + >> pmd = pmd_offset(pud, addr); >> - return (pte_t *) pmd; >> + if (!pmd_present(*pmd)) >> + return NULL; > > This breaks the current behaviour for swap entries in the pmd (for pud > is already broken but maybe no-one uses them). It is fixed in the > subsequent patch together with the pud but the series is no longer > bisectable. Maybe it's better if you fold the two patches together (or > change the order, though I'm not sure how readable it is). I missed the change in behaviour for pmd swap entries. I'll squash the two patches and re-post. Thanks for the review. -- 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