From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753586Ab2DUGw2 (ORCPT ); Sat, 21 Apr 2012 02:52:28 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:57061 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751022Ab2DUGw0 (ORCPT ); Sat, 21 Apr 2012 02:52:26 -0400 Message-ID: <4F925925.7040806@gmail.com> Date: Sat, 21 Apr 2012 14:52:21 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120216 Thunderbird/10.0.1 MIME-Version: 1.0 To: Marcelo Tosatti CC: Xiao Guangrong , Avi Kivity , LKML , KVM Subject: Re: [PATCH v3 2/9] KVM: MMU: abstract spte write-protect References: <4F911B74.4040305@linux.vnet.ibm.com> <4F911BAB.6000206@linux.vnet.ibm.com> <20120420213319.GA13817@amt.cnet> <4F922886.5060807@gmail.com> <20120421041854.GA2763@amt.cnet> In-Reply-To: <20120421041854.GA2763@amt.cnet> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/21/2012 12:18 PM, Marcelo Tosatti wrote: > On Sat, Apr 21, 2012 at 11:24:54AM +0800, Xiao Guangrong wrote: >> On 04/21/2012 05:33 AM, Marcelo Tosatti wrote: >> >> >>>> static bool >>>> __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, int level) >>>> { >>>> @@ -1050,24 +1078,13 @@ __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, int level) >>>> >>>> for (sptep = rmap_get_first(*rmapp, &iter); sptep;) { >>>> BUG_ON(!(*sptep & PT_PRESENT_MASK)); >>>> - rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep); >>>> - >>>> - if (!is_writable_pte(*sptep)) { >>>> - sptep = rmap_get_next(&iter); >>>> - continue; >>>> - } >>>> - >>>> - if (level == PT_PAGE_TABLE_LEVEL) { >>>> - mmu_spte_update(sptep, *sptep & ~PT_WRITABLE_MASK); >>>> - sptep = rmap_get_next(&iter); >>>> - } else { >>>> - BUG_ON(!is_large_pte(*sptep)); >>>> - drop_spte(kvm, sptep); >>>> - --kvm->stat.lpages; >>> >>> It is preferable to remove all large sptes including read-only ones, the >> >> >> It can cause page faults even if read memory on these large sptse. >> >> Actually, Avi suggested that make large writable spte to be readonly >> (not dropped) on this path. > > See commits e49146dce8c3dc6f4485c1904b6587855f393e71, > 38187c830cab84daecb41169948467f1f19317e3 for issues > with large read-only sptes. > Yes, we need check the code carefully when change writable spte to be read-only, let us discuss it in the separate patchset later. :)