From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752290Ab2EBF2t (ORCPT ); Wed, 2 May 2012 01:28:49 -0400 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:43252 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751453Ab2EBF2r (ORCPT ); Wed, 2 May 2012 01:28:47 -0400 Message-ID: <4FA0C607.5010002@linux.vnet.ibm.com> Date: Wed, 02 May 2012 13:28:39 +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: Avi Kivity , LKML , KVM Subject: Re: [PATCH v4 06/10] KVM: MMU: fast path of handling guest page fault References: <4F9776D2.7020506@linux.vnet.ibm.com> <4F9777A4.208@linux.vnet.ibm.com> <20120426234535.GA5057@amt.cnet> <4F9A3445.2060305@linux.vnet.ibm.com> <20120427145213.GB28796@amt.cnet> <4F9B89D9.9060307@linux.vnet.ibm.com> <20120501013459.GB10142@amt.cnet> In-Reply-To: <20120501013459.GB10142@amt.cnet> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12050205-5816-0000-0000-0000025EF3CC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/01/2012 09:34 AM, Marcelo Tosatti wrote: > > It is getting better, but not yet, there are still reads of sptep > scattered all over (as mentioned before, i think a pattern of read spte > once, work on top of that, atomically write and then deal with results > _everywhere_ (where mmu lock is held) is more consistent. > But we only need care the path which depends on is_writable_pte(), no? So, where call is_writable_pte() are spte_has_volatile_bits(), spte_write_protect() and set_spte(). I have changed these functions: In spte_has_volatile_bits(): static bool spte_has_volatile_bits(u64 spte) { + /* + * Always atomicly update spte if it can be updated + * out of mmu-lock. + */ + if (spte_can_lockless_update(spte)) + return true; + In spte_write_protect(): + spte = mmu_spte_update(sptep, spte); + + if (is_writable_pte(spte)) + *flush |= true; + The 'spte' is from atomically read-write (xchg). in set_spte(): set_pte: - mmu_spte_update(sptep, spte); + entry = mmu_spte_update(sptep, spte); /* * If we overwrite a writable spte with a read-only one we * should flush remote TLBs. Otherwise rmap_write_protect The 'entry' is also the latest value. > /* > * If we overwrite a writable spte with a read-only one we > * should 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. > */ > if (is_writable_pte(entry) && !is_writable_pte(*sptep)) > kvm_flush_remote_tlbs(vcpu->kvm); > > This is inconsistent with the above obviously. > 'entry' is not a problem since it is from atomically read-write as mentioned above, i need change this code to: /* * Optimization: for pte sync, if spte was writable the hash * lookup is unnecessary (and expensive). Write protection * is responsibility of mmu_get_page / kvm_sync_page. * Same reasoning can be applied to dirty page accounting. */ if (!can_unsync && is_writable_pte(entry) /* Use 'entry' instead of '*sptep'. */ goto set_pte ...... if (is_writable_pte(entry) && !is_writable_pte(spte)) /* Use 'spte' instead of '*sptep'. */ kvm_flush_remote_tlbs(vcpu->kvm);