From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH v3 5/5] KVM: Allow host IRQ sharing for passed-through PCI 2.3 devices Date: Wed, 03 Nov 2010 18:35:48 +0100 Message-ID: <4CD19D74.4080204@siemens.com> References: <628f014fb1efb8e2208db03d13198ba301a3a34c.1288771873.git.jan.kiszka@web.de> <20101103084320.GF6772@redhat.com> <1288799867.3045.149.camel@x201> <4CD19B96.2080603@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Alex Williamson , "Michael S. Tsirkin" , Avi Kivity , Marcelo Tosatti , kvm To: Jan Kiszka Return-path: Received: from david.siemens.de ([192.35.17.14]:18333 "EHLO david.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752903Ab0KCRgE (ORCPT ); Wed, 3 Nov 2010 13:36:04 -0400 In-Reply-To: <4CD19B96.2080603@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: Am 03.11.2010 18:27, Jan Kiszka wrote: > Am 03.11.2010 16:57, Alex Williamson wrote: >> On Wed, 2010-11-03 at 10:43 +0200, Michael S. Tsirkin wrote: >>> On Wed, Nov 03, 2010 at 09:11:16AM +0100, Jan Kiszka wrote: >>>> From: Jan Kiszka >>>> >>>> PCI 2.3 allows to generically disable IRQ sources at device level. This >>>> enables us to share IRQs of such devices between on the host side when >>>> passing them to a guest. This feature is optional, user space has to >>>> request it explicitly. >>>> >>>> Signed-off-by: Jan Kiszka >>> >>> >>> I just realized something. >>> With this patch, if guest ever looks at >>> interrupt disable bit, it will go crazy as that bit goes on/off by >>> itself. I guess we could have an ioctl to set/clear the bit on >>> device, and have qemu call that on config write into command/status >>> register. >>> >>> There's also something I don't completely unerstand with current code: >>> how does interrupt sharing work? E.g. can assigned and emulated >>> devices share an interrupt? >> >> I've been pondering this with VFIO too. There it seems to work, even >> when I enable irqfd. The VFIO kernel/qemu driver needs to filter EOIs >> based on whether the interrupt was actually asserted by the device, but >> I think we're likely relying somewhat on interrupts being reasserted to >> help us keep everything serviced. > > I don't think this filtering exists. The ack notifier that is fired on > EOI matches the GSI, hitting anyone who is registered. > > I think the problem is that, while user space properly or's the input of > all PCI devices on a IRQ line (e.g. in piix3_set_irq), kernel-side users > apparently prefer to mess directly with the irqchip. Unless I'm missing > something, that is long broken. No, it's actually or'ed in the kernel as well: kvm_irq_line_state. So, any issue remaining? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux