From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] [PATCH] qemu: msi irq allocation api Date: Thu, 21 May 2009 15:38:56 +0300 Message-ID: <4A154B60.4080701@redhat.com> References: <20090520162130.GA22109@redhat.com> <200905211301.52089.paul@codesourcery.com> <4A154432.1060808@redhat.com> <200905211329.41578.paul@codesourcery.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: qemu-devel@nongnu.org, Carsten Otte , kvm@vger.kernel.org, "Michael S. Tsirkin" , Rusty Russell , virtualization@lists.linux-foundation.org, Christian Borntraeger To: Paul Brook Return-path: Received: from mx2.redhat.com ([66.187.237.31]:52779 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750746AbZEUMlH (ORCPT ); Thu, 21 May 2009 08:41:07 -0400 In-Reply-To: <200905211329.41578.paul@codesourcery.com> Sender: kvm-owner@vger.kernel.org List-ID: Paul Brook wrote: >> Instead of writing directly, let's abstract it behind a qemu_set_irq(). >> This is easier for device authors. The default implementation of the >> irq callback could write to apic memory, while for kvm we can directly >> trigger the interrupt via the kvm APIs. >> > > I'm still not convinced. > > A tight coupling between PCI devices and the APIC is just going to cause us > problems later one. I'm going to come back to the fact that these are memory > writes so once we get IOMMU support they will presumably be subject to > remapping by that, just like any other memory access. > I'm not suggesting the qemu_irq will extend all the way to the apic. Think of it as connecting the device core with its interrupt unit. > Even ignoring that, qemu_irq isn't really the right interface. A MSI is a one- > off event, not a level state. OTOH stl_phys is exactly the right interface. > The qemu_irq callback should do an stl_phys(). The device is happy since it's using the same API it uses for non-MSI. The APIC is happy since it isn't connected directly to the device. stl_phys() is happy since it sees more traffic and can serve more ads. kvm is happy since it can hijack the callback to throw the interrupt directly into the kernel. > The KVM interface should be contained within the APIC implementation. > Tricky, but doable. -- error compiling committee.c: too many arguments to function