From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753943Ab3EMLGr (ORCPT ); Mon, 13 May 2013 07:06:47 -0400 Received: from smtp.citrix.com ([66.165.176.89]:15461 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751419Ab3EMLGq (ORCPT ); Mon, 13 May 2013 07:06:46 -0400 X-IronPort-AV: E=Sophos;i="4.87,662,1363132800"; d="scan'208";a="24810966" Date: Mon, 13 May 2013 12:06:43 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Konrad Rzeszutek Wilk CC: Zhenzhong Duan , Stefano Stabellini , "xen-devel@lists.xensource.com" , "linux-kernel@vger.kernel.org" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Yuval Shaia , Feng Jin , Chien Yen Subject: Re: [PATCH] xen: reuse the same pirq allocated when driver load first time In-Reply-To: <20130510185339.GD2562@phenom.dumpdata.com> Message-ID: References: <518A0A50.1020705@oracle.com> <20130510185339.GD2562@phenom.dumpdata.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 10 May 2013, Konrad Rzeszutek Wilk wrote: > On Wed, May 08, 2013 at 04:18:24PM +0800, Zhenzhong Duan wrote: > > When driver load and unload in a loop, pirq will exhaust finally. > > Try to use the same pirq which was already mapped and binded at first time > > So what happens if I unload and reload two drivers in random order? > > > when driver loaded. > > > > Read pirq from msix entry and test if data is XEN_PIRQ_MSI_DATA > > xen_irq_from_pirq(pirq) < 0 checking is wrong as irq will be freed > > when driver unload, it's always true in second load. > > If my understanding is right the issue at hand is that the caching > information about the pirq disappears once the driver has been > unloaded b/c the event's irq-info is removed (as the driver is > unloaded and free_irq is called). > > Stefano, > Is there a specific write to the MSI structure that would cause the > hypervisor to drop the PIRQ? Or a nice hypercall to "free" an > PIRQ in usage? We already have a "free PIRQ" hypercall, it's called PHYSDEVOP_unmap_pirq and should be called by QEMU. Linux should disable the MSI bit in the PCI config options of the device: pci_disable_msi -> pci_msi_shutdown -> msi_set_enable(0) That should cause QEMU to issue a xc_physdev_unmap_pirq that actually unmaps the pirq. If it doesn't, it's a bug :) > I presume that on the first load the msg.data value is > ALWAYS != XEN_PIRQ_MSI_DATA right? Is that somethign we can ALWAYS > depend? Or is there a possibility that it could be that when the > PCI device is unplugged from one guest and plugged in another? > > Could we use PHYSDEVOP_irq_status_query to figure out if the PIRQ > has been already allocated? Ah, does not look like it. > > I am a bit worried about depending on just msg.data to tells us > whether the device had been initialized before. Data comes from QEMU, I think it is zeroed at init time.