Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753510AbbFXPq3 (ORCPT ); Wed, 24 Jun 2015 11:46:29 -0400 Received: from 8bytes.org ([81.169.241.247]:39759 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752405AbbFXPqS (ORCPT ); Wed, 24 Jun 2015 11:46:18 -0400 Date: Wed, 24 Jun 2015 17:46:16 +0200 From: Joerg Roedel To: Alex Williamson Cc: "Wu, Feng" , Eric Auger , Avi Kivity , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "pbonzini@redhat.com" , "mtosatti@redhat.com" Subject: Re: [v4 08/16] KVM: kvm-vfio: User API for IRQ forwarding Message-ID: <20150624154616.GB18569@8bytes.org> References: <1434019912-15423-9-git-send-email-feng.wu@intel.com> <5579E884.3040500@gmail.com> <1434123695.4927.304.camel@redhat.com> <557B2994.1070900@gmail.com> <1434135815.4927.308.camel@redhat.com> <557EFA7F.9010209@linaro.org> <1434386702.4927.391.camel@redhat.com> <1434657848.3700.83.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1434657848.3700.83.camel@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2440 Lines: 59 On Thu, Jun 18, 2015 at 02:04:08PM -0600, Alex Williamson wrote: > There are plenty of details to be filled in, I also need to fill plenty of details in my head first, so here are some suggestions based on my current understanding. Please don't hesitate to correct me if where I got something wrong. So first I totally agree that the handling of PI/non-PI configurations should be transparent to user-space. I read a bit through the VT-d spec, and my understanding of posted interrupts so far is that: 1) Each VCPU gets a PI-Descriptor with its pending Posted Interrupts. This descriptor needs to be updated when a VCPU is migrated to another PCPU and should thus be under control of KVM. This is similar to the vAPIC backing page in the AMD version of this, except that the PCPU routing information is stored somewhere else on AMD. 2) As long as the VCPU runs the IRTEs are configured for posting, when the VCPU goes to sleep the old remapped entry is established again. So when the VCPU sleeps the interrupt would get routed to VFIO and forwarded through the eventfd. This would be different to the AMD version, where we have a running bit. When this is clear the IOMMU will trigger an event in its event-log. This might need special handling in VFIO ('might' because VFIO does not need to forward the interrupt, it just needs to make sure the VCPU wakes up). Please correct me if my understanding of the Intel version is wrong. So most of the data structures the IOMMU reads for this need to be updated from KVM code (either x86-generic or AMD/Intel specific code), as KVM has the information about VCPU load/unload and the IRQ routing. What KVM needs from VFIO are the informations about the physical interrupts, and it makes total sense to attach them as metadata to the eventfd. But the problems start at how this metadata should look like. It would be good to have some generic description, but not sure if this is possible. Otherwise this metadata would need to be requested by VFIO from the IOMMU driver and passed on to KVM, which it then passes back to the IOMMU driver. Or something like that. Joerg -- 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/