From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:41214 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754733AbdARLIh (ORCPT ); Wed, 18 Jan 2017 06:08:37 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Steve Capper , Huang Shijie , Catalin Marinas Subject: [PATCH 4.9 118/120] arm64: hugetlb: remove the wrong pmd check in find_num_contig() Date: Wed, 18 Jan 2017 11:47:16 +0100 Message-Id: <20170118104652.927429376@linuxfoundation.org> In-Reply-To: <20170118104648.120216880@linuxfoundation.org> References: <20170118104648.120216880@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Huang Shijie commit 20156ce2365d61beaa6f5a78a7a789044e0e7acc upstream. The find_num_contig() will return 1 when the pmd is not present. It will cause a kernel dead loop in the following scenaro: 1.) pmd entry is not present. 2.) the page fault occurs: ... hugetlb_fault() --> hugetlb_no_page() --> set_huge_pte_at() 3.) set_huge_pte_at() will only set the first PMD entry, since the find_num_contig just return 1 in this case. So the PMD entries are all empty except the first one. 4.) when kernel accesses the address mapped by the second PMD entry, a new page fault occurs: ... hugetlb_fault() --> huge_ptep_set_access_flags() The second PMD entry is still empty now. 5.) When the kernel returns, the access will cause a page fault again. The kernel will run like the "4)" above. We will see a dead loop since here. The dead loop is caught in the 32M hugetlb page (2M PMD + Contiguous bit). This patch removes wrong pmd check, and fixes this dead loop. This patch also removes the redundant checks for PGD/PUD in the find_num_contig(). Acked-by: Steve Capper Signed-off-by: Huang Shijie Reviewed-by: Catalin Marinas Signed-off-by: Catalin Marinas Signed-off-by: Greg Kroah-Hartman --- arch/arm64/mm/hugetlbpage.c | 12 ------------ 1 file changed, 12 deletions(-) --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -51,20 +51,8 @@ static int find_num_contig(struct mm_str *pgsize = PAGE_SIZE; if (!pte_cont(pte)) return 1; - if (!pgd_present(*pgd)) { - VM_BUG_ON(!pgd_present(*pgd)); - return 1; - } pud = pud_offset(pgd, addr); - if (!pud_present(*pud)) { - VM_BUG_ON(!pud_present(*pud)); - return 1; - } pmd = pmd_offset(pud, addr); - if (!pmd_present(*pmd)) { - VM_BUG_ON(!pmd_present(*pmd)); - return 1; - } if ((pte_t *)pmd == ptep) { *pgsize = PMD_SIZE; return CONT_PMDS;