From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758892Ab2IEPPI (ORCPT ); Wed, 5 Sep 2012 11:15:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:63193 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751318Ab2IEPPF (ORCPT ); Wed, 5 Sep 2012 11:15:05 -0400 Message-ID: <50476C76.6020008@redhat.com> Date: Wed, 05 Sep 2012 18:15:02 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: Alex Williamson , gleb@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd References: <20120821190800.24958.74812.stgit@bling.home> <20120821192903.24958.90138.stgit@bling.home> <504765B9.7010406@redhat.com> <20120905150707.GA11058@redhat.com> In-Reply-To: <20120905150707.GA11058@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/05/2012 06:07 PM, Michael S. Tsirkin wrote: > On Wed, Sep 05, 2012 at 05:46:17PM +0300, Avi Kivity wrote: >> On 08/21/2012 10:29 PM, Alex Williamson wrote: >> > KVM_IRQFD currently uses the reserved KVM_USERSPACE_IRQ_SOURCE_ID >> > which is also shared with userspace injection methods like >> > KVM_IRQ_LINE. This can cause a conflict if an irqfd triggers on >> > a GSI asserted through KVM_IRQ_LINE. Move irqfd to it's own >> > reserved IRQ source ID. Add a capability for userspace to test >> > for this fix. >> >> I don't think we need a cap, rather a backport if we identify real cases >> where an edge gsi is shared among several devices. Otherwise it is just >> a theoretical bug before level irqfd is introduced. > > In that case, I think it's safer to preserve the "bug" as is: we are > changing userspace-visible behaviour for edge interrupts otherwise. > For example if userspace uses kvm_irq_line for an edge > interrupt, set it to 1, previously it could then > continue to send any number of interrupts with irqfd, > now it can't. If anyone did that, they should have reported a bug, since they surely didn't expect edges if the line was held high. > > Basically the logical OR functionality of source IDs > does not make sense for edge. Edge is only interpreted at the ioapic or pic input; the line is just a line (an open collector line that ORs anything connected to it, or an equivalent). > > How about we do > if (flags&RESAMPLE) > source_id = USERSPACE > else > source_id = IRQFD Okay if we identify something that depends on the bug, otherwise not. -- error compiling committee.c: too many arguments to function