From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755535Ab2DERzG (ORCPT ); Thu, 5 Apr 2012 13:55:06 -0400 Received: from mail-iy0-f174.google.com ([209.85.210.174]:46938 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752389Ab2DERzD (ORCPT ); Thu, 5 Apr 2012 13:55:03 -0400 Message-ID: <4F7DDC6C.90304@gmail.com> Date: Fri, 06 Apr 2012 01:54:52 +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: Avi Kivity CC: Xiao Guangrong , Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH 08/13] KVM: MMU: fask check whether page is writable References: <4F742951.7080003@linux.vnet.ibm.com> <4F742A74.1050304@linux.vnet.ibm.com> <4F7879A1.2020301@redhat.com> In-Reply-To: <4F7879A1.2020301@redhat.com> 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 Hi Avi, Thanks very much for your review! Sorry for the delay reply since i was on vacation. On 04/01/2012 11:52 PM, Avi Kivity wrote: > On 03/29/2012 11:25 AM, Xiao Guangrong wrote: >> Using PTE_LIST_WRITE_PROTECT bit in rmap store the write-protect status to >> avoid unnecessary shadow page walking >> >> Also if no shadow page is indirect, the page is write-free >> >> >> @@ -2262,6 +2291,9 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn, >> } >> if (need_unsync) >> kvm_unsync_pages(vcpu, gfn); >> + >> + *rmap &= ~PTE_LIST_WRITE_PROTECT; >> + >> > > So what are the rules for PTE_LIST_WRITE_PROTECT? Is is a cache for the > mmu_need_write_protect? > > I'd like to understand it, I guess it can be set while write protection > is unneeded, and cleared on the next check? > Yes, it is used as a cache for mmu_need_write_protect. When the gfn is protected by sync sp or read-only host page we set this bit, and it is be cleared when the sp become unsync or host page becomes writable. > Maybe split into two functions, one the normal mmu_need_write_protect > (but renamed) and a new mmu_need_write_protect(), with locked and > unlocked variants, calling the old one. > Okay, i will split it by introducing a new function named mmu_unsync_gfn_sp which checks whether sp can become unsync and unsync sp if it is allowed under the protection of mmu-lock.