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 3C836C433DB for ; Wed, 17 Feb 2021 15:01:42 +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 E66E364E28 for ; Wed, 17 Feb 2021 15:01:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E66E364E28 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com 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.86310.161955 (Exim 4.92) (envelope-from ) id 1lCOKb-0001JP-Jh; Wed, 17 Feb 2021 15:01:33 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 86310.161955; Wed, 17 Feb 2021 15:01:33 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lCOKb-0001JI-Gc; Wed, 17 Feb 2021 15:01:33 +0000 Received: by outflank-mailman (input) for mailman id 86310; Wed, 17 Feb 2021 15:01:32 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lCOKa-0001JD-Ej for xen-devel@lists.xenproject.org; Wed, 17 Feb 2021 15:01:32 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id f981051a-7bad-430d-a71a-ae8792356cb3; Wed, 17 Feb 2021 15:01:31 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A5B0CB8FB; Wed, 17 Feb 2021 15:01:30 +0000 (UTC) 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" X-Inumbo-ID: f981051a-7bad-430d-a71a-ae8792356cb3 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1613574090; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XlcbOFN/qMdHxITM+PVmddFB6cOmVw5dejK6K51LolI=; b=FS1iGIboZm/U7U2+XCcEC5N9I/3YxiV67EeRH2I8NxEGTk3khhfkOPHG7tWwTMXZ+z+H6Y cM5f2Qccs7C0V18WRZ5WgfZZOiZO2yplNQZz9I5ZOgquxhWjPUGaiUrNaymqvy6PpoUTYC S6CtRZx2YWWhHHdB7QJaSukbLz0GLSo= Subject: Re: [for-4.15][PATCH v3 2/3] xen/x86: iommu: Ignore IOMMU mapping requests when a domain is dying To: Julien Grall 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> <20210217142458.3769-3-julien@xen.org> From: Jan Beulich Message-ID: <20f68b12-a767-b1d3-a3dd-9f92172def5f@suse.com> Date: Wed, 17 Feb 2021 16:01:29 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210217142458.3769-3-julien@xen.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 17.02.2021 15:24, Julien Grall wrote: > From: Julien Grall > > The new x86 IOMMU page-tables allocator will release the pages when > relinquishing the domain resources. However, this is not sufficient > when the domain is dying because nothing prevents page-table to be > allocated. > > Currently page-table allocations can only happen from iommu_map(). As > the domain is dying, there is no good reason to continue to modify the > IOMMU page-tables. While I agree this to be the case right now, I'm not sure it is a good idea to build on it (in that you leave the unmap paths untouched). Imo there's a fair chance this would be overlooked at the point super page mappings get introduced (which has been long overdue), and I thought prior discussion had lead to a possible approach without risking use-after-free due to squashed unmap requests. > --- a/xen/drivers/passthrough/x86/iommu.c > +++ b/xen/drivers/passthrough/x86/iommu.c > @@ -273,6 +273,9 @@ int iommu_free_pgtables(struct domain *d) > /* > * 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. > + * > + * After this call, no more IOMMU mapping can happen. > + * > */ > hd->platform_ops->clear_root_pgtable(d); I.e. you utilize the call in place of spin_barrier(). Maybe worth saying in the comment? Also, nit: Stray blank comment line. Jan