From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751936AbaIJOBI (ORCPT ); Wed, 10 Sep 2014 10:01:08 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:57967 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751084AbaIJOBG (ORCPT ); Wed, 10 Sep 2014 10:01:06 -0400 Date: Wed, 10 Sep 2014 17:01:01 +0300 From: Gleb Natapov To: tangchen Cc: mtosatti@redhat.com, nadav.amit@gmail.com, jan.kiszka@web.de, kvm@vger.kernel.org, laijs@cn.fujitsu.com, isimatu.yasuaki@jp.fujitsu.com, guz.fnst@cn.fujitsu.com, linux-kernel@vger.kernel.org, Paolo Bonzini Subject: Re: [PATCH v4 4/6] kvm, mem-hotplug: Reload L1' apic access page on migration in vcpu_enter_guest(). Message-ID: <20140910140100.GE25317@minantech.com> References: <1409134661-27916-1-git-send-email-tangchen@cn.fujitsu.com> <1409134661-27916-5-git-send-email-tangchen@cn.fujitsu.com> <20140902160005.GA26540@minantech.com> <54067206.7050303@cn.fujitsu.com> <20140903150448.GJ18167@minantech.com> <540EA883.9060206@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <540EA883.9060206@cn.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 09, 2014 at 03:13:07PM +0800, tangchen wrote: > Hi Gleb, > > On 09/03/2014 11:04 PM, Gleb Natapov wrote: > >On Wed, Sep 03, 2014 at 09:42:30AM +0800, tangchen wrote: > >>Hi Gleb, > >> > >>On 09/03/2014 12:00 AM, Gleb Natapov wrote: > >>>...... > >>>+static void vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu) > >>>+{ > >>>+ /* > >>>+ * apic access page could be migrated. When the page is being migrated, > >>>+ * GUP will wait till the migrate entry is replaced with the new pte > >>>+ * entry pointing to the new page. > >>>+ */ > >>>+ vcpu->kvm->arch.apic_access_page = gfn_to_page(vcpu->kvm, > >>>+ APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT); > >>>+ kvm_x86_ops->set_apic_access_page_addr(vcpu->kvm, > >>>+ page_to_phys(vcpu->kvm->arch.apic_access_page)); > >>>I am a little bit worried that here all vcpus write to vcpu->kvm->arch.apic_access_page > >>>without any locking. It is probably benign since pointer write is atomic on x86. Paolo? > >>> > >>>Do we even need apic_access_page? Why not call > >>> gfn_to_page(APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT) > >>> put_page() > >>>on rare occasions we need to know its address? > >>Isn't it a necessary item defined in hardware spec ? > >> > >vcpu->kvm->arch.apic_access_page? No. This is internal kvm data structure. > > > >>I didn't read intel spec deeply, but according to the code, the page's > >>address is > >>written into vmcs. And it made me think that we cannnot remove it. > >> > >We cannot remove writing of apic page address into vmcs, but this is not done by > >assigning to vcpu->kvm->arch.apic_access_page, but by vmwrite in set_apic_access_page_addr(). > > OK, I'll try to remove kvm->arch.apic_access_page and send a patch for it > soon. > > BTW, if you don't have objection to the first two patches, would you please > help to > commit them first ? > I acked them and CCed Paolo to this reply. I hope he will look at the series too. -- Gleb.