Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753439Ab3EMSVQ (ORCPT ); Mon, 13 May 2013 14:21:16 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:51936 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751230Ab3EMSVP (ORCPT ); Mon, 13 May 2013 14:21:15 -0400 Date: Mon, 13 May 2013 14:20:55 -0400 From: Konrad Rzeszutek Wilk To: Stefano Stabellini Cc: Zhenzhong Duan , "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 Message-ID: <20130513182055.GC14177@phenom.dumpdata.com> References: <518A0A50.1020705@oracle.com> <20130510185339.GD2562@phenom.dumpdata.com> <20130513140749.GQ6811@phenom.dumpdata.com> <20130513161714.GC10401@phenom.dumpdata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet22.oracle.com [141.146.126.238] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4545 Lines: 95 On Mon, May 13, 2013 at 06:24:46PM +0100, Stefano Stabellini wrote: > On Mon, 13 May 2013, Konrad Rzeszutek Wilk wrote: > > On Mon, May 13, 2013 at 03:50:52PM +0100, Stefano Stabellini wrote: > > > On Mon, 13 May 2013, Konrad Rzeszutek Wilk wrote: > > > > On Mon, May 13, 2013 at 12:06:43PM +0100, Stefano Stabellini wrote: > > > > > 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. > > > > > > > > Considering that we call function that allocates (PHYSDEVOP_get_free_pirq) > > > > it in the Linux kernel (and not in QEMU), perhaps that should be done in the > > > > Linux kernel as part of xen_destroy_irq()? Or would that confuse QEMU? > > > > > > I think it would confuse QEMU. It is probably better to let the unmap > > > being handled by it. > > > > > > > > > > It looks like QEMU only does that hypercall (via xc_physdev_unmap_pirq) > > > > unregister_real_device which is only called during pci unplug? > > > > > > You are right! I would think that this behaviour is erroneous unless it > > > was done on purpose to avoid allocating MSIs twice. > > > If that is the case we would need to do something similar in Linux too. > > > > > > I think that the issue is the mismatch between QEMU's and Linux's > > > behaviours: either both should be allocating MSIs once, or they should > > > both be allocating and deallocating MSIs every time the driver is loaded > > > and unloaded. > > > > Right. But we also have the scenario that QEMU and Linux are going to > > be out of sync. So we need fixes in both places - I think. > > QEMU is the owner of the pirq, in fact it is the one that creates and > destroys the mapping. I think that the right place to fix this problem > is in QEMU, the ABI would be much cleaner as a result. As a side effect > we don't need to make any changes in Linux. You do. You need to remove the PHYSDEVOP_get_free_pirq call in that case. > > > > > > > > > Linux should disable the MSI bit in the PCI config options of the > > > > > device: > > > > > > > > > > pci_disable_msi -> pci_msi_shutdown -> msi_set_enable(0) > > > > > > > > Zhenzhong, does it do that? Looking at the driver it certainly seems that way. > > > > > > > > > > That should cause QEMU to issue a xc_physdev_unmap_pirq that actually > > > > > unmaps the pirq. If it doesn't, it's a bug :) > > > > > > > > It doesn't do that. So two bugs: > > > > - QEMU doing that > > > > - Linux kernel doing the hypercall as well. > > > > > > At first sight I also thought that the Linux kernel was issuing > > > PHYSDEVOP_unmap_pirq too but actually Linux is only doing it if > > > xen_initial_domain(). > > > > That seems like an easy fix. Just do 'if (xen_initial_domain() > > || xen_hvm_domain())'. I think the only one we cannot do it for > > is 'xen_pv_domain()' (so PCI in PV guests) as the "owner" of the PIRQ is > > actually dom0. > > We could do that and it might be easier than changing QEMU, but I think > it would be more clear and consistent if QEMU was the one to do the > unmapping. And allocating the PIRQ? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/