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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 3E8B4C433E6 for ; Wed, 17 Feb 2021 16:48:26 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 EFF3E64E33 for ; Wed, 17 Feb 2021 16:48:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EFF3E64E33 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.86367.162138 (Exim 4.92) (envelope-from ) id 1lCPzt-00045v-KS; Wed, 17 Feb 2021 16:48:17 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 86367.162138; Wed, 17 Feb 2021 16:48:17 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lCPzt-00045o-H5; Wed, 17 Feb 2021 16:48:17 +0000 Received: by outflank-mailman (input) for mailman id 86367; Wed, 17 Feb 2021 16:48:16 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lCPzs-00045I-Ea for xen-devel@lists.xenproject.org; Wed, 17 Feb 2021 16:48:16 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lCPzp-0007YB-Ta; Wed, 17 Feb 2021 16:48:13 +0000 Received: from [54.239.6.185] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1lCPzp-0000CD-Mk; Wed, 17 Feb 2021 16:48:13 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=KLnzYZP1FGPH1cvVhn/Z/3hV4pR+fGuD5Tn7xqVIhEA=; b=T27ee3qb/OpaNGh+U2AuzM7bCJ o5GIkYKcW9fLQe/Dfjn1//0n/ELR2qLkxfEU9/fNtL5/QCb+p49HpM4+u4FBU+bnpUWZVO79xmllW 5EDY2KYAiheXIJejsmHtzQhBlHFUKcEMbWT4ohw7qhqDdZDnMPTBvID9UjGoCLtn1GdI=; Subject: Re: [for-4.15][PATCH v3 1/3] xen/iommu: x86: Clear the root page-table before freeing the page-tables To: Jan Beulich Cc: hongyxia@amazon.co.uk, iwj@xenproject.org, Julien Grall , Andrew Cooper , Kevin Tian , Paul Durrant , xen-devel@lists.xenproject.org References: <20210217142458.3769-1-julien@xen.org> <20210217142458.3769-2-julien@xen.org> <87548d76-36fa-f587-0137-6806280617ad@xen.org> <334ee115-c710-88c7-aa27-975bdb6c6912@suse.com> From: Julien Grall Message-ID: Date: Wed, 17 Feb 2021 16:48:11 +0000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <334ee115-c710-88c7-aa27-975bdb6c6912@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit On 17/02/2021 15:17, Jan Beulich wrote: > On 17.02.2021 16:00, Julien Grall wrote: >> Hi Jan, >> >> On 17/02/2021 14:54, Jan Beulich wrote: >>> On 17.02.2021 15:24, Julien Grall wrote: >>>> --- a/xen/drivers/passthrough/x86/iommu.c >>>> +++ b/xen/drivers/passthrough/x86/iommu.c >>>> @@ -267,6 +267,15 @@ int iommu_free_pgtables(struct domain *d) >>>> struct page_info *pg; >>>> unsigned int done = 0; >>>> >>>> + if ( !is_iommu_enabled(d) ) >>>> + return 0; >>>> + >>>> + /* >>>> + * Pages will be moved to the free list below. So we want to >>>> + * clear the root page-table to avoid any potential use after-free. >>>> + */ >>>> + hd->platform_ops->clear_root_pgtable(d); >>> >>> Taking amd_iommu_alloc_root() as example, is this really correct >>> prior to what is now patch 2? >> >> Yes, there are no more use-after-free... > > And this is because of ...? The necessary lock isn't being held > here, so on another CPU allocation of a new root and then of new > page tables could happen before you make enough progress here, > and hence it looks to me as if there might then still be pages > which get freed while present in the page tables (and hence > accessible by devices). Ah yes. I forgot that now patch #3 is not first anymore. I can move again patch #3 first, although I know you dislike the approach taken there... Cheers, -- Julien Grall