From: Paul Brook Subject: Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions Date: Wed, 10 Jun 2009 15:07:34 +0100 Message-ID: <200906101507.39823.paul@codesourcery.com> References: <200906100019.59981.paul@codesourcery.com> <20090610094604.GD6844@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: qemu-devel@nongnu.org, Avi Kivity , Carsten Otte , kvm@vger.kernel.org, Rusty Russell , virtualization@lists.linux-foundation.org, Christian Borntraeger , Blue Swirl To: "Michael S. Tsirkin" Return-path: Received: from mail.codesourcery.com ([65.74.133.4]:44170 "EHLO mail.codesourcery.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755107AbZFJOHj (ORCPT ); Wed, 10 Jun 2009 10:07:39 -0400 In-Reply-To: <20090610094604.GD6844@redhat.com> Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: > > > Note that platform must set a flag to declare MSI supported. > > > For PC this will be set by APIC. > > > > This sounds wrong. The device shouldn't know or care whether the system > > has a MSI capable interrupt controller. That's for the guest OS to figure > > out. > > You are right of course. In theory there's nothing that breaks if I > set this flag to on, on all platforms. OTOH if qemu emulates some > controller incorrectly, guest might misdetect MSI support in the > controller, and things will break horribly. > > It seems safer to have a flag that can be enabled by people > that know about a specific platform. No. The solution is to fix whatever is broken. If we really need to avoid MSI-X capable devices then that should be done explicity per-device. i.e. you have a different virtio-net device that does not use MSI-X. Paul