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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 D4784ECDFB3 for ; Mon, 16 Jul 2018 07:38:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9816320864 for ; Mon, 16 Jul 2018 07:38:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9816320864 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732800AbeGPIEb (ORCPT ); Mon, 16 Jul 2018 04:04:31 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:46918 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732677AbeGPIEa (ORCPT ); Mon, 16 Jul 2018 04:04:30 -0400 Received: from localhost (LFbn-1-12247-202.w90-92.abo.wanadoo.fr [90.92.61.202]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 96920CA1; Mon, 16 Jul 2018 07:38:28 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Christian Borntraeger , Martin Schwidefsky , Andrea Arcangeli , Mike Rapoport , Janosch Frank , David Hildenbrand , Cornelia Huck , Andrew Morton , Linus Torvalds Subject: [PATCH 4.17 35/67] mm: do not drop unused pages when userfaultd is running Date: Mon, 16 Jul 2018 09:35:04 +0200 Message-Id: <20180716073448.643250194@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180716073443.294323458@linuxfoundation.org> References: <20180716073443.294323458@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Borntraeger commit bce73e4842390f7b7309c8e253e139db71288ac3 upstream. KVM guests on s390 can notify the host of unused pages. This can result in pte_unused callbacks to be true for KVM guest memory. If a page is unused (checked with pte_unused) we might drop this page instead of paging it. This can have side-effects on userfaultd, when the page in question was already migrated: The next access of that page will trigger a fault and a user fault instead of faulting in a new and empty zero page. As QEMU does not expect a userfault on an already migrated page this migration will fail. The most straightforward solution is to ignore the pte_unused hint if a userfault context is active for this VMA. Link: http://lkml.kernel.org/r/20180703171854.63981-1-borntraeger@de.ibm.com Signed-off-by: Christian Borntraeger Cc: Martin Schwidefsky Cc: Andrea Arcangeli Cc: Mike Rapoport Cc: Janosch Frank Cc: David Hildenbrand Cc: Cornelia Huck Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/rmap.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- a/mm/rmap.c +++ b/mm/rmap.c @@ -64,6 +64,7 @@ #include #include #include +#include #include @@ -1481,11 +1482,16 @@ static bool try_to_unmap_one(struct page set_pte_at(mm, address, pvmw.pte, pteval); } - } else if (pte_unused(pteval)) { + } else if (pte_unused(pteval) && !userfaultfd_armed(vma)) { /* * The guest indicated that the page content is of no * interest anymore. Simply discard the pte, vmscan * will take care of the rest. + * A future reference will then fault in a new zero + * page. When userfaultfd is active, we must not drop + * this page though, as its main user (postcopy + * migration) will not expect userfaults on already + * copied pages. */ dec_mm_counter(mm, mm_counter(page)); /* We have to invalidate as we cleared the pte */