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 06AB2C433EF for ; Tue, 1 Mar 2022 02:55:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231887AbiCAC4d (ORCPT ); Mon, 28 Feb 2022 21:56:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229885AbiCAC4b (ORCPT ); Mon, 28 Feb 2022 21:56:31 -0500 Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12F222F026; Mon, 28 Feb 2022 18:55:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1646103352; x=1677639352; h=message-id:date:mime-version:cc:subject:to:references: from:in-reply-to:content-transfer-encoding; bh=/z7xcV6dl5VH6iMxyI/FmOZYADVup3Kf2UPfn1iS7uU=; b=WC7OMSMeOs4NLtfBcS/hP7TP9X4MgwzjjPwd/Vmlr5x3qRsg9TP5ONNp GKQ8ejVVR9Wl72dCrroXGPXm9N64Icc6zaU+U6ciFOqKmS3CqYr6toikd VQpTGzG+q0ZpvhRZ32hF8B8UI7tZr10ZBAdAEkYxT2/pzpqu4VobV4bY3 QPO3LdE1co+G4JMZEKSIOBanf2ULSKekfNxwxLMu0hA1g0rXEctcdtrQc M1D++CQoy6SFU//ZhUtpj9DJT8KKgW8hsjiHJyrxqe5OGahPUyKAkFCiM vPz36h1xC3/SaMJuZY/u6FpGaohE/IPnEWmCOhPhpDTB3iPRyuQej23GM g==; X-IronPort-AV: E=McAfee;i="6200,9189,10272"; a="253233751" X-IronPort-AV: E=Sophos;i="5.90,144,1643702400"; d="scan'208";a="253233751" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Feb 2022 18:55:51 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.90,144,1643702400"; d="scan'208";a="534724101" Received: from allen-box.sh.intel.com (HELO [10.239.159.118]) ([10.239.159.118]) by orsmga007.jf.intel.com with ESMTP; 28 Feb 2022 18:55:43 -0800 Message-ID: <80672557-59ab-8eb9-2fcf-d045ff52104b@linux.intel.com> Date: Tue, 1 Mar 2022 10:54:09 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Cc: baolu.lu@linux.intel.com, Greg Kroah-Hartman , Joerg Roedel , Alex Williamson , Bjorn Helgaas , Jason Gunthorpe , Christoph Hellwig , Kevin Tian , Ashok Raj , kvm@vger.kernel.org, rafael@kernel.org, David Airlie , linux-pci@vger.kernel.org, Thierry Reding , Diana Craciun , Dmitry Osipenko , Will Deacon , Stuart Yoder , Jonathan Hunter , Chaitanya Kulkarni , Dan Williams , Cornelia Huck , linux-kernel@vger.kernel.org, Li Yang , iommu@lists.linux-foundation.org, Jacob jun Pan , Daniel Vetter , Robin Murphy Subject: Re: [PATCH v7 06/11] PCI: portdrv: Set driver_managed_dma Content-Language: en-US To: Bjorn Helgaas References: <20220228195628.GA515785@bhelgaas> From: Lu Baolu In-Reply-To: <20220228195628.GA515785@bhelgaas> 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 Hi Bjorn, On 3/1/22 3:56 AM, Bjorn Helgaas wrote: > On Mon, Feb 28, 2022 at 08:50:51AM +0800, Lu Baolu wrote: >> If a switch lacks ACS P2P Request Redirect, a device below the switch can >> bypass the IOMMU and DMA directly to other devices below the switch, so >> all the downstream devices must be in the same IOMMU group as the switch >> itself. >> >> The existing VFIO framework allows the portdrv driver to be bound to the >> bridge while its downstream devices are assigned to user space. The >> pci_dma_configure() marks the IOMMU group as containing only devices >> with kernel drivers that manage DMA. Avoid this default behavior for the >> portdrv driver in order for compatibility with the current VFIO usage. > > It would be nice to explicitly say here how we can look at portdrv > (and pci_stub) and conclude that ".driver_managed_dma = true" is safe. > > Otherwise I won't know what kind of future change to portdrv might > make it unsafe. Fair enough. We can add below words: We achieve this by setting ".driver_managed_dma = true" in pci_driver structure. It is safe because the portdrv driver meets below criteria: - This driver doesn't use DMA, as you can't find any related calls like pci_set_master() or any kernel DMA API (dma_map_*() and etc.). - It doesn't use MMIO as you can't find ioremap() or similar calls. It's tolerant to userspace possibly also touching the same MMIO registers via P2P DMA access. > >> Suggested-by: Jason Gunthorpe >> Suggested-by: Kevin Tian >> Signed-off-by: Lu Baolu >> Reviewed-by: Jason Gunthorpe > > Acked-by: Bjorn Helgaas Thank you! Best regards, baolu > >> --- >> drivers/pci/pcie/portdrv_pci.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c >> index 35eca6277a96..6b2adb678c21 100644 >> --- a/drivers/pci/pcie/portdrv_pci.c >> +++ b/drivers/pci/pcie/portdrv_pci.c >> @@ -202,6 +202,8 @@ static struct pci_driver pcie_portdriver = { >> >> .err_handler = &pcie_portdrv_err_handler, >> >> + .driver_managed_dma = true, >> + >> .driver.pm = PCIE_PORTDRV_PM_OPS, >> }; >> >> -- >> 2.25.1 >> >> _______________________________________________ >> iommu mailing list >> iommu@lists.linux-foundation.org >> https://lists.linuxfoundation.org/mailman/listinfo/iommu