From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756201Ab0C3KCV (ORCPT ); Tue, 30 Mar 2010 06:02:21 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:52918 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752399Ab0C3KCU (ORCPT ); Tue, 30 Mar 2010 06:02:20 -0400 Message-ID: <4BB15B1A.7090901@cn.fujitsu.com> Date: Tue, 30 Mar 2010 09:59:54 +0800 From: Xiao Guangrong User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) MIME-Version: 1.0 To: Avi Kivity CC: Ingo Molnar , Marcelo Tosatti , Sheng Yang , KVM list , LKML Subject: [RFC] KVM MMU: thinking of shadow page cache 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 When we cached shadow page tables, one guest page table may have many shadow pages, take below case for example: (RO+U) ---> |------| __ |------| (W+U ) ---> | GP1 | | | GP2 | (W+P ) ---> |------| |--> |------| There have 3 kinds of permission mapping to GP1, so we should allocate 3 shadow pages for GP1 and 3 shadow pages for GP2. And it has 3 class permissions(R/W, U/S, X/NX) in x86's architecture, for the worst case, we should allocate 2^3 pages for every paging mapping level. This waste is caused by that we only set the permission bits in PTE, not in the middle mapping level. So, i think we can mapping guest page table's permission into cache shadow page table, then it can be shared between many shadow page tables if their map to the same gust physics address. For above case, we only need 2 pages. Any comments?