From: Punit Agrawal <punit.agrawal@arm.com> To: Andrew Morton <akpm@linux-foundation.org> Cc: Punit Agrawal <punit.agrawal@arm.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, 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 <mhocko@suse.com>, Mike Kravetz <mike.kravetz@oracle.com> Subject: [PATCH 1/1] mm/hugetlb: Make huge_pte_offset() consistent and document behaviour Date: Tue, 25 Jul 2017 16:41:14 +0100 [thread overview] Message-ID: <20170725154114.24131-2-punit.agrawal@arm.com> (raw) In-Reply-To: <20170725154114.24131-1-punit.agrawal@arm.com> 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@arm.com> --- 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
WARNING: multiple messages have this Message-ID (diff)
From: Punit Agrawal <punit.agrawal@arm.com> To: Andrew Morton <akpm@linux-foundation.org> Cc: Punit Agrawal <punit.agrawal@arm.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, 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 <mhocko@suse.com>, Mike Kravetz <mike.kravetz@oracle.com> Subject: [PATCH 1/1] mm/hugetlb: Make huge_pte_offset() consistent and document behaviour Date: Tue, 25 Jul 2017 16:41:14 +0100 [thread overview] Message-ID: <20170725154114.24131-2-punit.agrawal@arm.com> (raw) In-Reply-To: <20170725154114.24131-1-punit.agrawal@arm.com> 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@arm.com> --- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-07-25 15:41 UTC|newest] Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-07-25 15:41 [PATCH 0/1] Clarify huge_pte_offset() semantics Punit Agrawal 2017-07-25 15:41 ` Punit Agrawal 2017-07-25 15:41 ` Punit Agrawal [this message] 2017-07-25 15:41 ` [PATCH 1/1] mm/hugetlb: Make huge_pte_offset() consistent and document behaviour Punit Agrawal 2017-07-26 8:39 ` Catalin Marinas 2017-07-26 8:39 ` Catalin Marinas 2017-07-26 8:50 ` Michal Hocko 2017-07-26 8:50 ` Michal Hocko 2017-07-26 8:53 ` Michal Hocko 2017-07-26 8:53 ` Michal Hocko 2017-07-26 12:11 ` Punit Agrawal 2017-07-26 12:11 ` Punit Agrawal 2017-07-26 12:11 ` Punit Agrawal 2017-07-26 12:33 ` Michal Hocko 2017-07-26 12:33 ` Michal Hocko 2017-07-26 12:47 ` Michal Hocko 2017-07-26 12:47 ` Michal Hocko 2017-07-26 13:34 ` Punit Agrawal 2017-07-26 13:34 ` Punit Agrawal 2017-07-26 13:34 ` Punit Agrawal 2017-07-27 3:16 ` Mike Kravetz 2017-07-27 3:16 ` Mike Kravetz 2017-07-27 12:58 ` Punit Agrawal 2017-07-27 12:58 ` Punit Agrawal 2017-07-27 12:58 ` Punit Agrawal 2017-07-27 12:58 ` Punit Agrawal 2017-08-18 14:54 ` [PATCH v2] mm/hugetlb.c: make " Punit Agrawal 2017-08-18 14:54 ` Punit Agrawal 2017-08-18 14:54 ` Punit Agrawal 2017-08-18 14:54 ` Punit Agrawal 2017-08-18 21:29 ` Mike Kravetz 2017-08-18 21:29 ` Mike Kravetz 2017-08-21 18:07 ` Catalin Marinas 2017-08-21 18:07 ` Catalin Marinas 2017-08-21 21:30 ` Mike Kravetz 2017-08-21 21:30 ` Mike Kravetz 2017-08-22 15:32 ` Punit Agrawal 2017-08-22 15:32 ` Punit Agrawal 2017-08-22 10:11 ` Catalin Marinas 2017-08-22 10:11 ` Catalin Marinas 2017-08-30 7:49 ` Michal Hocko 2017-08-30 7:49 ` Michal Hocko
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20170725154114.24131-2-punit.agrawal@arm.com \ --to=punit.agrawal@arm.com \ --cc=akpm@linux-foundation.org \ --cc=catalin.marinas@arm.com \ --cc=kirill.shutemov@linux.intel.com \ --cc=linux-arch@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-mm@kvack.org \ --cc=mhocko@suse.com \ --cc=mike.kravetz@oracle.com \ --cc=n-horiguchi@ah.jp.nec.com \ --cc=steve.capper@arm.com \ --cc=will.deacon@arm.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.