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=-17.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 1ABCEC433E0 for ; Wed, 17 Feb 2021 11:38:49 +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 D3A9864DDA for ; Wed, 17 Feb 2021 11:38:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D3A9864DDA 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.86226.161718 (Exim 4.92) (envelope-from ) id 1lCLAG-0005h5-Gr; Wed, 17 Feb 2021 11:38:40 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 86226.161718; Wed, 17 Feb 2021 11:38:40 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lCLAG-0005gy-CT; Wed, 17 Feb 2021 11:38:40 +0000 Received: by outflank-mailman (input) for mailman id 86226; Wed, 17 Feb 2021 11:38:39 +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 1lCLAE-0005go-Vg for xen-devel@lists.xenproject.org; Wed, 17 Feb 2021 11:38:39 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 0c4b9658-75e6-40de-9758-2556c233326d; Wed, 17 Feb 2021 11:38:37 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 45D6CB125; Wed, 17 Feb 2021 11:38:36 +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: 0c4b9658-75e6-40de-9758-2556c233326d 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=1613561916; 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=1kg9CDmEonWqa5Cubbsh4CG5mab/QezBHryd96oV8Ss=; b=djwstGH2h+mp93vugv2X9BznSdSCrYeNP8nGyNq5Of9wF8m6tJ5XydblCH1lNSn4JtPs/Y l9TfzRU0zsY6tS9xer1DOj+5BpuiAi5NXXQmFPcIMgwVXdMCm8l7fvLwVS/U0D0gamdqNz 1KcPQu2JwtF1iud3Gee2KUE+6RVVyfs= Subject: Re: [PATCH 2/3] gnttab: bypass IOMMU (un)mapping when a domain is (un)mapping its own grant To: Julien Grall Cc: Andrew Cooper , George Dunlap , Ian Jackson , Stefano Stabellini , Wei Liu , Rahul Singh , "xen-devel@lists.xenproject.org" References: <156559d5-853a-5bb9-942b-f623627e0907@suse.com> <5bb4fba7-a10b-90c4-82f7-8cde6e8cacfb@suse.com> From: Jan Beulich Message-ID: <283d8514-16fb-8973-e395-0a86bf820306@suse.com> Date: Wed, 17 Feb 2021 12:38:35 +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 17.02.2021 12:03, Julien Grall wrote: > On 17/02/2021 10:46, Jan Beulich wrote: >> Mappings for a domain's own pages should already be present in the >> IOMMU. While installing the same mapping again is merely redundant (and >> inefficient), removing the mapping when the grant mapping gets removed >> is outright wrong in this case: The mapping was there before the map, so >> should remain in place after unmapping. >> >> This affects >> - Arm Dom0 in the direct mapped case, >> - x86 PV Dom0 in the "iommu=dom0-strict" / "dom0-iommu=strict" cases, >> - all x86 PV DomU-s, including driver domains. >> >> Reported-by: Rahul Singh >> Signed-off-by: Jan Beulich >> >> --- a/xen/common/grant_table.c >> +++ b/xen/common/grant_table.c >> @@ -1243,7 +1243,7 @@ map_grant_ref( >> goto undo_out; >> } >> >> - need_iommu = gnttab_need_iommu_mapping(ld); >> + need_iommu = ld != rd && gnttab_need_iommu_mapping(ld); > > AFAICT, the owner of the page may not always be rd. So do we want to > check against the owner instead? For the DomIO case - specifically not. And the DomCOW case can't happen when an IOMMU is in use. Did I overlook any other cases where the page may not be owned by rd? Jan