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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C4AAC433EF for ; Wed, 6 Apr 2022 14:38:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234299AbiDFOkj (ORCPT ); Wed, 6 Apr 2022 10:40:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48872 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235019AbiDFOkb (ORCPT ); Wed, 6 Apr 2022 10:40:31 -0400 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2324C458D17 for ; Wed, 6 Apr 2022 04:03:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1649242999; x=1680778999; h=message-id:date:mime-version:cc:subject:to:references: from:in-reply-to:content-transfer-encoding; bh=ZgeY5au0/JYbpMr1ByPbrAcDmwZzKH4hE93co6HLIk4=; b=Wjx+M5b7XH6ENZc7yg32fquctLHo7NY7fn570Ato6av34It3NIAWyrvT ARBdjwjbEv6j14NGe5RuBtmuouLMuLfSMn8+kqJYcG0By8RKSjchrqmGq Azszwj8YTNOsTonee84mHtLeDt2eS2ZaZM8L9OoSdhmFaY6SrGC4jWx2I 4riw5ew4S99QW2iZtFlco7X4Z6N715Ru/kQqWJZykUXikQQR8c1+qgeX0 x4ggShlSWKy3SS+PDgSx2PKIhvCp6PLZw2GMtmogWgYwCz+j8EQRdEIFs KW+gCg5JhHCfcrKnaf7///X60uKmyQl8VguY8m6J8U8Te7eRTT8R2Vmny g==; X-IronPort-AV: E=McAfee;i="6200,9189,10308"; a="260714140" X-IronPort-AV: E=Sophos;i="5.90,239,1643702400"; d="scan'208";a="260714140" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Apr 2022 04:03:18 -0700 X-IronPort-AV: E=Sophos;i="5.90,239,1643702400"; d="scan'208";a="570465683" Received: from blu2-mobl3.ccr.corp.intel.com (HELO [10.254.215.82]) ([10.254.215.82]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Apr 2022 04:03:14 -0700 Message-ID: Date: Wed, 6 Apr 2022 19:03:12 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Cc: baolu.lu@linux.intel.com, "Alex Williamson (alex.williamson@redhat.com)" , "Raj, Ashok" , Jean-Philippe Brucker , "linux-kernel@vger.kernel.org" , Christoph Hellwig , "iommu@lists.linux-foundation.org" , "Pan, Jacob jun" , Will Deacon , Robin Murphy Subject: Re: [PATCH RFC v2 02/11] iommu: Add iommu_group_singleton_lockdown() Content-Language: en-US To: "Tian, Kevin" , Jason Gunthorpe References: <20220329053800.3049561-1-baolu.lu@linux.intel.com> <20220329053800.3049561-3-baolu.lu@linux.intel.com> <20220329114259.GB1716663@nvidia.com> <20220330115820.GE1716663@nvidia.com> <20220330143008.GB2111031@nvidia.com> <821dc298-47fb-6d06-ba75-de5d62a97b7a@linux.intel.com> From: Lu Baolu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/4/6 18:44, Tian, Kevin wrote: >> From: Lu Baolu >> Sent: Wednesday, April 6, 2022 6:02 PM >> >> Hi Kevin, >> >> On 2022/4/2 15:12, Tian, Kevin wrote: >>>>>> Add a flag to the group that positively indicates the group can never >>>>>> have more than one member, even after hot plug. eg because it is >>>>>> impossible due to ACS, or lack of bridges, and so on. >>>>> OK, I see your point. It essentially refers to a singleton group which >>>>> is immutable to hotplug. >>>> Yes, known at creation time, not retroactively enforced because >>>> someone used SVA >>>> >>> We may check following conditions to set the immutable flag when >>> a new group is created for a device in pci_device_group(): >>> >>> 1) ACS is enabled in the upstream path of the device; >>> 2) the device is single function or ACS is enabled on a multi-function device; >>> 3) the device type is PCI_EXP_TYPE_ENDPOINT (thus no hotplug); >>> 4) no 'dma aliasing' on this device; >>> >>> The last one is a bit conservative as it also precludes a device which aliasing >>> dma due to quirks from being treated as a singleton group. But doing so >>> saves the effort on trying to separate different aliasing scenarios as defined >>> in pci_for_each_dma_alias(). Probably we can go this way as the first step. >>> >>> Once the flag is set on a group no other event can change it. If a new >>> identified device hits an existing singleton group in pci_device_group() >>> then it's a bug. >> >> How about below implementation? >> >> /* callback for pci_for_each_dma_alias() */ >> static int has_pci_alias(struct pci_dev *pdev, u16 alias, void *opaque) >> { >> return -EEXIST; >> } >> >> static bool pci_dev_is_immutably_isolated(struct pci_dev *pdev) >> { >> /* Skip bridges. */ >> if (pci_is_bridge(pdev)) >> return false; >> >> /* Either connect to root bridge or the ACS-enabled bridge. */ >> if (!pci_is_root_bus(pdev->bus) && >> !pci_acs_enabled(pdev->bus->self, REQ_ACS_FLAGS)) >> return false; > > it's not sufficient to just check the non-root bridge itself. This needs to > cover the entire path from the bridge to the root port, as pci_device_group() > does. Yes! You are right. > >> >> /* ACS is required for MFD. */ >> if (pdev->multifunction && !pci_acs_enabled(pdev, REQ_ACS_FLAGS)) >> return false; > > Above two checks be replaced by a simple check as below: > > if (!pci_acs_path_enabled(pdev, NULL, REQ_ACS_FLAGS)) > return false; If !pdev->multifunction, do we still need to start from the device itself? ACS is only for MFDs and bridges, do I understand it right? Do we need to consider the SRIOV case? > >> >> /* Make sure no PCI alias. */ >> if (pci_for_each_dma_alias(pdev, has_pci_alias, NULL)) >> return false; >> >> return true; >> } >> >> I didn't get why do we need to check the PCI_EXP_TYPE_ENDPOINT device >> type. Can you please elaborate a bit more? >> > > I didn't know there is a pci_is_bridge() facility thus be conservative > to restrict it to only endpoint device. If checking pci_is_bridge() alone > excludes any hotplug possibility, then it's definitely better. Okay! Thanks! > Thanks > Kevin Best regards, baolu