From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH v3 2/3] KVM: MMU: fix accessed bit set on prefault path Date: Tue, 30 Nov 2010 20:38:33 +0200 Message-ID: <20101130183833.GB2924@redhat.com> References: <4CF4C535.8080405@cn.fujitsu.com> <4CF4C587.7080000@cn.fujitsu.com> <20101130132915.GG2187@redhat.com> <4CF52BC6.9020401@cn.fujitsu.com> <20101130175005.GA2924@redhat.com> <4CF53F41.1040503@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , Marcelo Tosatti , LKML , KVM To: Xiao Guangrong Return-path: Content-Disposition: inline In-Reply-To: <4CF53F41.1040503@cn.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Wed, Dec 01, 2010 at 02:15:29AM +0800, Xiao Guangrong wrote: > On 12/01/2010 01:50 AM, Gleb Natapov wrote: > > On Wed, Dec 01, 2010 at 12:52:22AM +0800, Xiao Guangrong wrote: > >> On 11/30/2010 09:29 PM, Gleb Natapov wrote: > >> > >>>> + if (!shadow_accessed_mask) > >>>> + return; > >>>> + > >>> I don't get this. As far as I can see VMX inits shadow_accessed_mask to > >>> be zero if ept is enabled. This line here means that we never prefault with ept > >>> enabled. It is opposite from what it should be. > >>> > >> > >> Since it's no accessed bit on EPT, it's no way to distinguish between actually > >> accessed translations and prefault. > > Why is this a problem? We do what this page to not be evicted again > > since we expect it to be accessed. > > > > It can't avoid the page to be evicted again since the page is marked accessed only > when spte is droped or updated. I still do not understand why are you disabling prefault for ept. Why do you want to distinguish between actually accessed translations and prefauls? What problem are you trying to fix? -- Gleb.