From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH] do not free active mmu pages in free_mmu_pages() Date: Mon, 16 Mar 2009 23:20:10 +0200 Message-ID: <20090316212010.GC7898@redhat.com> References: <20090311100755.GA19724@redhat.com> <20090316201533.GA4477@amt.cnet> <20090316203401.GB7898@redhat.com> <20090316210152.GA5077@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: avi@redhat.com, marcelo@redhat.com, kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from mx2.redhat.com ([66.187.237.31]:53582 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755715AbZCPVX6 (ORCPT ); Mon, 16 Mar 2009 17:23:58 -0400 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id n2GLNukD031657 for ; Mon, 16 Mar 2009 17:23:56 -0400 Content-Disposition: inline In-Reply-To: <20090316210152.GA5077@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On Mon, Mar 16, 2009 at 06:01:52PM -0300, Marcelo Tosatti wrote: > On Mon, Mar 16, 2009 at 10:34:01PM +0200, Gleb Natapov wrote: > > > Doesnt the vm shutdown path rely on the while loop you removed to free > > > all shadow pages before freeing the mmu kmem caches, if mmu notifiers > > > is disabled? > > > > > Shouldn't mmu_free_roots() on all vcpus clear all mmu pages? > > No. It only zaps the present root on every vcpu, but not > the children. > > > > And how harmful is that loop? Zaps the entire cache on cpu hotunplug? > > > > > KVM doesn't support vcpu destruction, but destruction is called anyway > > on various error conditions. The one that easy to trigger is to create > > vcpu with the same id simultaneously from two threads. The result is > > OOPs in random places. > > mmu_lock should be held there, and apparently it is not. > Yeah, my first solution was to add mmu_lock, but why function that gets vcpu as an input should destroy data structure that is global for the VM. There is kvm_mmu_zap_all() that does same thing (well almost) and also does proper locking. Shouldn't it be called during VM destruction instead? -- Gleb.