From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756095Ab0KPU3E (ORCPT ); Tue, 16 Nov 2010 15:29:04 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39940 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755923Ab0KPU3C (ORCPT ); Tue, 16 Nov 2010 15:29:02 -0500 Date: Tue, 16 Nov 2010 18:24:15 -0200 From: Marcelo Tosatti To: Xiao Guangrong Cc: Avi Kivity , LKML , KVM Subject: Re: [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO Message-ID: <20101116202414.GA24156@amt.cnet> References: <4CDD173E.8010706@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4CDD173E.8010706@cn.fujitsu.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 12, 2010 at 06:30:22PM +0800, Xiao Guangrong wrote: > We just need flush tlb if overwrite a writable spte with a read-only one > > Signed-off-by: Xiao Guangrong > --- > arch/x86/kvm/mmu.c | 19 +++++++++---------- > 1 files changed, 9 insertions(+), 10 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 4b6d54c..1a93ab4 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -2044,6 +2044,15 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, > if (pte_access & ACC_WRITE_MASK) > mark_page_dirty(vcpu->kvm, gfn); > > + /* > + * If we overwrite a writable spte with a read-only one, > + * flush remote TLBs. Otherwise rmap_write_protect will > + * find a read-only spte, even though the writable spte > + * might be cached on a CPU's TLB. > + */ > + else if (is_writable_pte(*sptep)) > + ret = 1; > + The return value of set_spte indicates whether the gfn being mapped to was write protected, not if a TLB flush is necessary. > set_pte: > update_spte(sptep, spte); > done: > @@ -2084,16 +2093,6 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep, > spte_to_pfn(*sptep), pfn); > drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte); > kvm_flush_remote_tlbs(vcpu->kvm); > - /* > - * If we overwrite a writable spte with a read-only one, > - * drop it and flush remote TLBs. Otherwise rmap_write_protect > - * will find a read-only spte, even though the writable spte > - * might be cached on a CPU's TLB. > - */ > - } else if (is_writable_pte(*sptep) && > - (!(pte_access & ACC_WRITE_MASK) || !dirty)) { > - drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte); > - kvm_flush_remote_tlbs(vcpu->kvm); > } else > was_rmapped = 1; And here, flush will only happen if overwrite is RW->RO.