From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:48596 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751267AbdARH0M (ORCPT ); Wed, 18 Jan 2017 02:26:12 -0500 Subject: Patch "arm64: hugetlb: remove the wrong pmd check in find_num_contig()" has been added to the 4.9-stable tree To: shijie.huang@arm.com, catalin.marinas@arm.com, gregkh@linuxfoundation.org, steve.capper@arm.com Cc: , From: Date: Wed, 18 Jan 2017 08:26:08 +0100 Message-ID: <148472436812427@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled arm64: hugetlb: remove the wrong pmd check in find_num_contig() to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: arm64-hugetlb-remove-the-wrong-pmd-check-in-find_num_contig.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 20156ce2365d61beaa6f5a78a7a789044e0e7acc Mon Sep 17 00:00:00 2001 From: Huang Shijie Date: Tue, 8 Nov 2016 13:44:38 +0800 Subject: arm64: hugetlb: remove the wrong pmd check in find_num_contig() 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; Patches currently in stable-queue which might be from shijie.huang@arm.com are queue-4.9/arm64-hugetlb-fix-the-wrong-address-for-several-functions.patch queue-4.9/arm64-hugetlb-remove-the-wrong-pmd-check-in-find_num_contig.patch queue-4.9/arm64-hugetlb-fix-the-wrong-return-value-for-huge_ptep_set_access_flags.patch