Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753009AbaF0Iu0 (ORCPT ); Fri, 27 Jun 2014 04:50:26 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:65305 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756AbaF0IuX (ORCPT ); Fri, 27 Jun 2014 04:50:23 -0400 Date: Fri, 27 Jun 2014 09:47:22 +0100 From: Will Deacon To: Alex Williamson Cc: "Chalamarla, Tirumalesh" , Joerg Roedel , "kvm@vger.kernel.org" , open list , "stuart.yoder@freescale.com" , "iommu@lists.linux-foundation.org" , "tech@virtualopensystems.com" , "kvmarm@lists.cs.columbia.edu" , "moderated list:ARM SMMU DRIVER" , marc.zyngier@arm.com Subject: Re: [RFC PATCH v6 04/20] iommu/arm-smmu: add capability IOMMU_CAP_INTR_REMAP Message-ID: <20140627084722.GB26276@arm.com> References: <20140616151329.GQ16758@arm.com> <20140616152157.GB31771@8bytes.org> <20140616152526.GR16758@arm.com> <20140616153832.GC31771@8bytes.org> <9353770066894e85809e1e443b71d1cd@BY2PR07MB203.namprd07.prod.outlook.com> <748dccbbd3284521af4659ccbbb11453@BY2PR07MB203.namprd07.prod.outlook.com> <1403809223.31091.137.camel@ul30vt.home> <1403811384.31091.151.camel@ul30vt.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1403811384.31091.151.camel@ul30vt.home> 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 On Thu, Jun 26, 2014 at 08:36:24PM +0100, Alex Williamson wrote: > On Thu, 2014-06-26 at 19:10 +0000, Chalamarla, Tirumalesh wrote: > > Thanks for the clarification Alex, That’s exactly my point, why are we > > relying on QEMU or something else to emulate the MSI space when we can > > directly give access to devices using ITS (of course with a small > > emulation code). This way we are also benefited from all ITS services > > like VCPU migration etc. > > I have no idea what ITS is. ITS is the MSI doorbell for GICv3 (ARM's latest interrupt controller). I agree that we will need an ITS emulation if we want to use MSIs in the guest, and I believe that Marc (CC'd) had already started thinking about that. > > What about non QEMU VFIO users, for example, if I wanted to use VFIO to > > assign a device to a user process I don't need to depend on QEMU. I > > thought this is one of the main goals of vfio to make it independent of > > hypervisors. > > Where did QEMU become a requirement? Maybe I'm missing something in the > ARM part of the conversation that got chopped off, but this is exactly > why we have the VFIO/QEMU split that we do. VFIO provides basic > virtualization for config space and restricts access to other areas that > users shouldn't be allowed to change. QEMU is just one example of a > userspace VFIO driver. QEMU takes the decomposed device exposed through > the VFIO ABI and re-creates a PCI device out of it. VFIO itself has no > dependency on QEMU. Thanks, I also don't understand the QEMU part here. The MSI emulation would be in the kernel, just like the GICv2 emulation that we already have. For userspace drivers, wouldn't you just use eventfd rather than bother with emulating MSIs? Finally, the interrupt remapping part is about the SMMU preventing MSI writes to arbitrary portions of the host address space. The ITS is about routing interrupts to CPUs. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/