Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753853AbbGNUFc (ORCPT ); Tue, 14 Jul 2015 16:05:32 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:30699 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753713AbbGNUF1 (ORCPT ); Tue, 14 Jul 2015 16:05:27 -0400 Message-ID: <55A56B48.4060605@oracle.com> Date: Tue, 14 Jul 2015 16:04:24 -0400 From: Boris Ostrovsky User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Thomas Gleixner CC: Yanmin Zhang , Joerg Roedel , Peter Zijlstra , LKML , Ingo Molnar , Peter Anvin , xen-devel , Borislav Petkov , xiao jin Subject: Re: [Xen-devel] [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down References: <20150705170530.849428850@linutronix.de> <20150705171102.063519515@linutronix.de> <55A51F10.7010407@oracle.com> <55A532C2.4080306@oracle.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2115 Lines: 56 On 07/14/2015 01:32 PM, Thomas Gleixner wrote: > On Tue, 14 Jul 2015, Boris Ostrovsky wrote: >> On 07/14/2015 11:44 AM, Thomas Gleixner wrote: >>> On Tue, 14 Jul 2015, Boris Ostrovsky wrote: >>>>> Prevent allocation and freeing of interrupt descriptors accross cpu >>>>> hotplug. >>>> This breaks Xen guests that allocate interrupt descriptors in .cpu_up(). >>> And where exactly does XEN allocate those descriptors? >> xen_cpu_up() >> xen_setup_timer() >> bind_virq_to_irqhandler() >> bind_virq_to_irq() >> xen_allocate_irq_dynamic() >> xen_allocate_irqs_dynamic() >> irq_alloc_descs() >> >> >> There is also a similar pass via xen_cpu_up() -> xen_smp_intr_init() > Sigh. > >>> >>>> Any chance this locking can be moved into arch code? >>> No. > The issue here is that all architectures need that protection and just > Xen does irq allocations in cpu_up. > > So moving that protection into architecture code is not really an > option. > >>>> Otherwise we will need to have something like arch_post_cpu_up() >>>> after the lock is released. > I'm not sure, that this will work. You probably want to do this in the > cpu prepare stage, i.e. before calling __cpu_up(). For PV guests (the ones that use xen_cpu_up()) it will work either before or after __cpu_up(). At least my (somewhat limited) testing didn't show any problems so far. However, HVM CPUs use xen_hvm_cpu_up() and if you read comments there you will see that xen_smp_intr_init() needs to be called before native_cpu_up() but xen_init_lock_cpu() (which eventually calls irq_alloc_descs()) needs to be called after. I think I can split xen_init_lock_cpu() so that the part that needs to be called after will avoid going into irq core code. And then the rest will go into arch_cpu_prepare(). -boris -- 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/