From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Xu Subject: Re: [PATCH v1 01/22] KVM: x86: race between KVM_SET_GSI_ROUTING and KVM_CREATE_IRQCHIP Date: Wed, 15 Mar 2017 17:28:19 +0800 Message-ID: <20170315092819.GF5971@pxdev.xzpeter.org> References: <20170314133450.13259-1-david@redhat.com> <20170314133450.13259-2-david@redhat.com> <20170315062442.GI12964@pxdev.xzpeter.org> <4295fa2c-217d-dce0-e749-175abf41c1a4@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: kvm@vger.kernel.org, Paolo Bonzini , rkrcmar@redhat.com To: David Hildenbrand Return-path: Received: from mx1.redhat.com ([209.132.183.28]:35260 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751694AbdCOJ2Z (ORCPT ); Wed, 15 Mar 2017 05:28:25 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1128F80464 for ; Wed, 15 Mar 2017 09:28:25 +0000 (UTC) Content-Disposition: inline In-Reply-To: <4295fa2c-217d-dce0-e749-175abf41c1a4@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Mar 15, 2017 at 10:19:53AM +0100, David Hildenbrand wrote: > Am 15.03.2017 um 07:24 schrieb Peter Xu: > > On Tue, Mar 14, 2017 at 02:34:29PM +0100, David Hildenbrand wrote: > >> Avoid races between KVM_SET_GSI_ROUTING and KVM_CREATE_IRQCHIP by taking > >> the kvm->lock when setting up routes. > >> > >> If KVM_CREATE_IRQCHIP fails, KVM_SET_GSI_ROUTING could have already set > >> up routes pointing at pic/ioapic, being silently removed already. > >> > >> Signed-off-by: David Hildenbrand > >> --- > >> virt/kvm/kvm_main.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > >> index a17d787..ad0f8b2 100644 > >> --- a/virt/kvm/kvm_main.c > >> +++ b/virt/kvm/kvm_main.c > >> @@ -3079,8 +3079,11 @@ static long kvm_vm_ioctl(struct file *filp, > >> routing.nr * sizeof(*entries))) > >> goto out_free_irq_routing; > >> } > >> + /* avoid races with KVM_CREATE_IRQCHIP on x86 */ > >> + mutex_lock(&kvm->lock); > >> r = kvm_set_irq_routing(kvm, entries, routing.nr, > >> routing.flags); > >> + mutex_unlock(&kvm->lock); > >> out_free_irq_routing: > >> vfree(entries); > >> break; > >> -- > >> 2.9.3 > >> > > > > Out of my curiousity: do we have a use case that these two operations > > might collapse (KVM_CREATE_IRQCHIP and KVM_SET_GSI_ROUTING)? Or is > > this patch only for the sake of security? > > Just for the sake of security. I think, in general such calls are not > supposed to be done in parallel. But of course, user space can. I see. > > > > > Another thing to mention is that, I guess adding this lock will > > benefit KVM_CAP_SPLIT_IRQCHIP as well, maybe nice to mention it too in > > the commit message. No worth a repost for this single reason though. > > > > I added > > "Also, as a side effect, this patch makes sure that KVM_SET_GSI_ROUTING > and KVM_CAP_SPLIT_IRQCHIP cannot run in parallel." Yeah it looks better. Thanks! -- peterx