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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 1D3B4C433E0 for ; Fri, 19 Feb 2021 08:50:08 +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 ACD8864E38 for ; Fri, 19 Feb 2021 08:50:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ACD8864E38 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.86808.163225 (Exim 4.92) (envelope-from ) id 1lD1U6-0001Qu-Ie; Fri, 19 Feb 2021 08:49:58 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 86808.163225; Fri, 19 Feb 2021 08:49:58 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD1U6-0001Qn-FT; Fri, 19 Feb 2021 08:49:58 +0000 Received: by outflank-mailman (input) for mailman id 86808; Fri, 19 Feb 2021 08:49:56 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lD1U4-0001Qi-9b for xen-devel@lists.xenproject.org; Fri, 19 Feb 2021 08:49:56 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id e7f6ec65-a373-4d26-97bb-d7e28b308470; Fri, 19 Feb 2021 08:49:55 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A25D8AD29; Fri, 19 Feb 2021 08:49:54 +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: e7f6ec65-a373-4d26-97bb-d7e28b308470 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=1613724594; 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=WwfJzREW3w3iAgJqzedGFL8X5T4KF6M7SnNM51vcU58=; b=rjeZ1ZffG+WtIWL+4gazAEU9QcXAo6xQksKJI6IIFLBDRIO6ZuIEDwHn77ZS1HSsSS+zeB AMDjZ0gcHOcMl7jaQQFhhKGP1C/eR27CSCxgPetez8x2pCXlaFxC02X8VX70pYJGoX5bYs xNemxZv5GQ3zOGSavNlWDwvZmj+/ybY= 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 , xen-devel@lists.xenproject.org, Paul Durrant References: <20210217142458.3769-1-julien@xen.org> <20210217142458.3769-3-julien@xen.org> <20f68b12-a767-b1d3-a3dd-9f92172def5f@suse.com> <268f1991-bacb-c888-04c0-0e4cf670b6b5@suse.com> From: Jan Beulich Message-ID: Date: Fri, 19 Feb 2021 09:49:54 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 18.02.2021 14:25, Julien Grall wrote: > Hi, > > On 18/02/2021 13:05, Jan Beulich wrote: >> On 17.02.2021 17:07, Julien Grall wrote: >>> On 17/02/2021 15:01, Jan Beulich wrote: >>>> 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). >>> >>> I don't build on that assumption. See next patch. >> >> Yet as said there that patch makes unmapping perhaps more fragile, >> by introducing a latent error source into the path. > > I still don't see what latent error my patch will introduce. Allocation > of page-tables are not guarantee to succeed. > > So are you implying that a code may rely on the page allocation to succeed? I'm implying that failure to split a superpage may have unknown consequences. Since we make no use of superpages when not sharing page tables, I call this a latent issue which may go unnoticed for quite some time once no longer latent. Jan