From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [patch 2/3] KVM: x86: disallow KVM_{SET,GET}_LAPIC without in kernel irqchip Date: Wed, 28 Oct 2009 12:32:24 +0200 Message-ID: <20091028103223.GB24238@redhat.com> References: <20091027151042.118902183@redhat.com> <20091027151125.345664553@redhat.com> <20091027175026.GC14421@redhat.com> <4AE80F90.8010303@redhat.com> <20091028102041.GA24238@redhat.com> <20091028103039.GU29477@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , Marcelo Tosatti , kvm , stable@kernel.org To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:4425 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753430AbZJ1KfD (ORCPT ); Wed, 28 Oct 2009 06:35:03 -0400 Content-Disposition: inline In-Reply-To: <20091028103039.GU29477@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Oct 28, 2009 at 12:30:39PM +0200, Gleb Natapov wrote: > On Wed, Oct 28, 2009 at 12:20:42PM +0200, Michael S. Tsirkin wrote: > > On Wed, Oct 28, 2009 at 11:32:00AM +0200, Avi Kivity wrote: > > > On 10/27/2009 07:50 PM, Michael S. Tsirkin wrote: > > >> Can the value of irqchip_in_kernel be changed by userspace > > >> after we have checked it? If yes, this check won't help ... > > >> > > > > > > A change from false to true is possible, but not the reverse. > > > > Hmm. If we want to rely on this, we have to play with > > memory barriers to write/read it. Doable, but hard to get right. > Why? If userspace is so racy that it tries to use vpic while other > thread creates it let it fail and burn in hell. Yes but reading uninitialized memory in kernel can lead to host kernel crashes. > > Can we always have the irqchip object exist? > > It doesn't use a lot of memory, does it? > > Maybe have it inline, save an extra indirection on > > fastpath ... > > > > > -- > > > error compiling committee.c: too many arguments to function > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > Gleb.