From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E88F9C49360 for ; Tue, 8 Jun 2021 18:43:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE13C61883 for ; Tue, 8 Jun 2021 18:43:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235924AbhFHSpe (ORCPT ); Tue, 8 Jun 2021 14:45:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:37652 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235108AbhFHSlW (ORCPT ); Tue, 8 Jun 2021 14:41:22 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 59BFA61439; Tue, 8 Jun 2021 18:35:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1623177314; bh=JMC0ZDdJYN5mh4Dd9SGXk9gzGcYabtw+NxbZdtMdboo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kOk9rDyf4oYToeAu7QAHxlGmeqhTURHiOosPKUWfUwWD+x97Uf/4K2kJg7/gS9Odf XQE93cgnVwwDjR8zVtSQGv59KX1AJouGr8YX5rd6yC/EMIASChHqMOJrUpAP4IArTh 49gBebqHA+yTBOUhn1DqoTNnqJzesFla6y1BoT/8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mina Almasry , Mike Kravetz , Axel Rasmussen , Peter Xu , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 4.19 39/58] mm, hugetlb: fix simple resv_huge_pages underflow on UFFDIO_COPY Date: Tue, 8 Jun 2021 20:27:20 +0200 Message-Id: <20210608175933.560654165@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210608175932.263480586@linuxfoundation.org> References: <20210608175932.263480586@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Mina Almasry [ Upstream commit d84cf06e3dd8c5c5b547b5d8931015fc536678e5 ] The userfaultfd hugetlb tests cause a resv_huge_pages underflow. This happens when hugetlb_mcopy_atomic_pte() is called with !is_continue on an index for which we already have a page in the cache. When this happens, we allocate a second page, double consuming the reservation, and then fail to insert the page into the cache and return -EEXIST. To fix this, we first check if there is a page in the cache which already consumed the reservation, and return -EEXIST immediately if so. There is still a rare condition where we fail to copy the page contents AND race with a call for hugetlb_no_page() for this index and again we will underflow resv_huge_pages. That is fixed in a more complicated patch not targeted for -stable. Test: Hacked the code locally such that resv_huge_pages underflows produce a warning, then: ./tools/testing/selftests/vm/userfaultfd hugetlb_shared 10 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success ./tools/testing/selftests/vm/userfaultfd hugetlb 10 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success Both tests succeed and produce no warnings. After the test runs number of free/resv hugepages is correct. [mike.kravetz@oracle.com: changelog fixes] Link: https://lkml.kernel.org/r/20210528004649.85298-1-almasrymina@google.com Fixes: 8fb5debc5fcd ("userfaultfd: hugetlbfs: add hugetlb_mcopy_atomic_pte for userfaultfd support") Signed-off-by: Mina Almasry Reviewed-by: Mike Kravetz Cc: Axel Rasmussen Cc: Peter Xu Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/hugetlb.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2f769a661568..c69f12e4c149 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4154,10 +4154,20 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, struct page *page; if (!*pagep) { - ret = -ENOMEM; + /* If a page already exists, then it's UFFDIO_COPY for + * a non-missing case. Return -EEXIST. + */ + if (vm_shared && + hugetlbfs_pagecache_present(h, dst_vma, dst_addr)) { + ret = -EEXIST; + goto out; + } + page = alloc_huge_page(dst_vma, dst_addr, 0); - if (IS_ERR(page)) + if (IS_ERR(page)) { + ret = -ENOMEM; goto out; + } ret = copy_huge_page_from_user(page, (const void __user *) src_addr, -- 2.30.2