From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753553Ab1G0Gas (ORCPT ); Wed, 27 Jul 2011 02:30:48 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:62588 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752178Ab1G0Gap (ORCPT ); Wed, 27 Jul 2011 02:30:45 -0400 Message-ID: <4E2FB10B.9080805@cn.fujitsu.com> Date: Wed, 27 Jul 2011 14:32:43 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Thunderbird/3.1.10 MIME-Version: 1.0 To: Gleb Natapov CC: Avi Kivity , Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH 03/11] KVM: x86: fast emulate repeat string write instructions References: <4E2EA3DB.7040403@cn.fujitsu.com> <4E2EA476.9070607@cn.fujitsu.com> <20110726122710.GM4404@redhat.com> <4E2F6E48.7030802@cn.fujitsu.com> <20110727042602.GA7966@redhat.com> In-Reply-To: <20110727042602.GA7966@redhat.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-07-27 14:29:48, Serialize by Router on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-07-27 14:29:49, Serialize complete at 2011-07-27 14:29:49 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/27/2011 12:26 PM, Gleb Natapov wrote: > On Wed, Jul 27, 2011 at 09:47:52AM +0800, Xiao Guangrong wrote: >> On 07/26/2011 08:27 PM, Gleb Natapov wrote: >>> On Tue, Jul 26, 2011 at 07:26:46PM +0800, Xiao Guangrong wrote: >>>> We usually use repeat string instructions to clear the page, for example, >>> By "we" do you mean Linux guest? >>> >> >> I do not know other guests except linux, but, generally rep instruction is >> not used to update a page table which is been using. >> >>>> we call memset to clear a page table, stosb is used in this function, and >>>> repeated for 1024 times, that means we should occupy mmu lock for 1024 times >>>> and walking shadow page cache for 1024 times, it is terrible >>>> >>>> In fact, if it is the repeat string instructions emulated and it is not a >>>> IO/MMIO access, we can zap all the corresponding shadow pages and return to the >>>> guest, then the mapping can became writable and directly write the page >>>> >> >> >>> So this patch does two independent things as far as I can see. First it >>> stops reentering guest if rep instruction is done on memory and second >> >> No. >> Oppositely, it enters guest as soon as possible if rep instruction is done >> on memory ;-) > Oops. Indeed. I read it other way around. So why not just return > X86EMUL_UNHANDLEABLE from emulator_write_emulated_onepage() which should > have the same effect? > It seams not, the count register(RCX) is not decreased, and redundant work need to be done by handling EMULATION_FAILED. So, emulator_write_emulated_onepage() is not a good place i think. :-)