Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964884AbdGTJTH (ORCPT ); Thu, 20 Jul 2017 05:19:07 -0400 Received: from foss.arm.com ([217.140.101.70]:49988 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933731AbdGTJTF (ORCPT ); Thu, 20 Jul 2017 05:19:05 -0400 Date: Thu, 20 Jul 2017 10:19:10 +0100 From: Will Deacon To: Anup Patel Cc: Robin Murphy , Joerg Roedel , Baptiste Reynal , Alex Williamson , Scott Branden , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux-foundation.org, kvm@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com Subject: Re: [PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking iommu_present() Message-ID: <20170720091909.GC17837@arm.com> References: <1500525154-5200-1-git-send-email-anup.patel@broadcom.com> <1500525154-5200-2-git-send-email-anup.patel@broadcom.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1500525154-5200-2-git-send-email-anup.patel@broadcom.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 554 Lines: 14 On Thu, Jul 20, 2017 at 10:02:33AM +0530, Anup Patel wrote: > Not allowing No-IOMMU mode for devices already having > iommu_ops on their bus is very conservative. > > We now have IOMMU (such as ARM SMMU) which can bypass > transcations when IOMMU is not configured for a given > device. In addition, it is not necessary to have all > devices on bus to be upstream to an IOMMU on that bus. How does the SMMU know to bypass in these cases? As I explained before, the driver-specific command line option is the wrong way to go about arranging this. Will