From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756734Ab2K0Xmz (ORCPT ); Tue, 27 Nov 2012 18:42:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:24121 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751951Ab2K0Xmy (ORCPT ); Tue, 27 Nov 2012 18:42:54 -0500 Date: Tue, 27 Nov 2012 21:32:46 -0200 From: Marcelo Tosatti To: Xiao Guangrong Cc: Avi Kivity , LKML , KVM Subject: Re: [PATCH 2/3] KVM: x86: let reexecute_instruction work for tdp Message-ID: <20121127233246.GB8295@amt.cnet> References: <50AAC77C.8040505@linux.vnet.ibm.com> <50AAC7CE.2050506@linux.vnet.ibm.com> <20121126223712.GA10634@amt.cnet> <50B42FC7.2080805@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50B42FC7.2080805@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 27, 2012 at 11:13:11AM +0800, Xiao Guangrong wrote: > >> +static bool reexecute_instruction(struct kvm_vcpu *vcpu, unsigned long cr2) > >> { > >> - gpa_t gpa; > >> + gpa_t gpa = cr2; > >> pfn_t pfn; > >> > >> - if (tdp_enabled) > >> + if (!ACCESS_ONCE(vcpu->kvm->arch.indirect_shadow_pages)) > >> return false; > > > > How is indirect_shadow_pages protected? Why is ACCESS_ONCE() being used > > to read it? > > Hi Marcelo, > > It is protected by mmu-lock for it only be changed when mmu-lock is hold. And > ACCESS_ONCE is used on read path avoiding magic optimization from compiler. Please switch to mmu_lock protection, there is no reason to have access to this variable locklessly - not performance critical. For example, there is no use of barriers when modifying the variable.