From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754271AbZECQ7z (ORCPT ); Sun, 3 May 2009 12:59:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752059AbZECQ7o (ORCPT ); Sun, 3 May 2009 12:59:44 -0400 Received: from mx2.redhat.com ([66.187.237.31]:59583 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751944AbZECQ7n (ORCPT ); Sun, 3 May 2009 12:59:43 -0400 Message-ID: <49FDCD7C.7070605@redhat.com> Date: Sun, 03 May 2009 19:59:40 +0300 From: Avi Kivity User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: Gregory Haskins , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, davidel@xmailserver.org Subject: Re: [KVM PATCH v3 2/2] kvm: add support for irqfd via eventfd-notification interface References: <20090427182540.6646.96740.stgit@dev.haskins.net> <20090427183334.6646.90800.stgit@dev.haskins.net> <20090430130708.GA13763@redhat.com> In-Reply-To: <20090430130708.GA13763@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michael S. Tsirkin wrote: > On Mon, Apr 27, 2009 at 02:33:34PM -0400, Gregory Haskins wrote: > >> This allows an eventfd to be registered as an irq source with a guest. Any >> signaling operation on the eventfd (via userspace or kernel) will inject >> the registered GSI at the next available window. >> >> Signed-off-by: Gregory Haskins >> > > If we ever want to use this with e.g. MSI-X emulation in guest, and want > to be stricly compliant to MSI-X, we'll need a way for guest to mask > interrupts, and for host to report that a masked interrupt is pending. > Ideally, all this will be doable with a couple of mmapped pages to avoid > vmexits/system calls. > > We could do this in two ways: - move msix entry emulation into the kernel - require the device to support replacing its irqfd, and juggle it like so: - guest disables msi - replace device model fd with eventfd belonging to us - when the device fires its eventfd, set the irq pending bit - guest enables msi - if the pending bit is set, fire the interrupt? - replace device model fd with the real irqfd I'm leaning towards the latter, though it's not an easy call. >> +static void >> +irqfd_inject(struct work_struct *work) >> +{ >> + struct _irqfd *irqfd = container_of(work, struct _irqfd, work); >> + struct kvm *kvm = irqfd->kvm; >> + >> + mutex_lock(&kvm->lock); >> + kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1); >> + kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0); >> + mutex_unlock(&kvm->lock); >> > > This will do weird stuff (deliver the irq twice) if the irq is > MSI/MSI-X. I know this was discussed already and is a temporary > shortcut, but maybe add a comment that we really want kvm_toggle_irq, > so that we won't forget? > If so, that's a bug. MSI should ignore kvm_set_irq(..., 0). -- error compiling committee.c: too many arguments to function