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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 B8BA6C3A5A9 for ; Sat, 18 Apr 2020 12:10:29 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8A28521D79 for ; Sat, 18 Apr 2020 12:10:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8A28521D79 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 4805E2010E; Sat, 18 Apr 2020 12:10:29 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 8sSraq-YpYIm; Sat, 18 Apr 2020 12:10:28 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id 848E32010A; Sat, 18 Apr 2020 12:10:28 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 69A68C089F; Sat, 18 Apr 2020 12:10:28 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1CE97C0172 for ; Sat, 18 Apr 2020 12:10:27 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 065D7876C7 for ; Sat, 18 Apr 2020 12:10:27 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 4Rh15zhILMYl for ; Sat, 18 Apr 2020 12:10:25 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from theia.8bytes.org (8bytes.org [81.169.241.247]) by whitealder.osuosl.org (Postfix) with ESMTPS id B4469876C5 for ; Sat, 18 Apr 2020 12:10:25 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id 945EE342; Sat, 18 Apr 2020 14:10:23 +0200 (CEST) Date: Sat, 18 Apr 2020 14:10:22 +0200 From: Joerg Roedel To: Qian Cai Subject: Re: [RFC PATCH] iommu/amd: fix a race in fetch_pte() Message-ID: <20200418121022.GA6113@8bytes.org> References: <20200407021246.10941-1-cai@lca.pw> <7664E2E7-04D4-44C3-AB7E-A4334CDEC373@lca.pw> <20200408141915.GJ3103@8bytes.org> <527B0883-F59D-4C7A-8102-743872801EFC@lca.pw> <4FAF3A63-8DC8-4489-B5FE-95B716EF25AE@lca.pw> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4FAF3A63-8DC8-4489-B5FE-95B716EF25AE@lca.pw> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Thu, Apr 16, 2020 at 09:42:41PM -0400, Qian Cai wrote: > So, this is still not enough that would still trigger storage driver offline under > memory pressure for a bit longer. It looks to me that in fetch_pte() there are > could still racy? Yes, your patch still looks racy. You need to atomically read domain->pt_root to a stack variable and derive the pt_root pointer and the mode from that variable instead of domain->pt_root directly. If you read the domain->pt_root twice there could still be an update between the two reads. Probably the lock in increase_address_space() can also be avoided if pt_root is updated using cmpxchg()? Regards, Joerg _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu