From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67E53C433E6 for ; Tue, 16 Feb 2021 03:31:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2EEF564E00 for ; Tue, 16 Feb 2021 03:31:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229787AbhBPDbD (ORCPT ); Mon, 15 Feb 2021 22:31:03 -0500 Received: from out30-45.freemail.mail.aliyun.com ([115.124.30.45]:40303 "EHLO out30-45.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229617AbhBPDbA (ORCPT ); Mon, 15 Feb 2021 22:31:00 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R181e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01424;MF=tianjia.zhang@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0UOk85wU_1613446213; Received: from 30.25.189.44(mailfrom:tianjia.zhang@linux.alibaba.com fp:SMTPD_---0UOk85wU_1613446213) by smtp.aliyun-inc.com(127.0.0.1); Tue, 16 Feb 2021 11:30:14 +0800 Subject: Re: [PATCH v3 3/5] x86/sgx: Optimize the free_cnt count in sgx_epc_section To: Jarkko Sakkinen Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Sean Christopherson , Shuah Khan , x86@kernel.org, linux-sgx@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Jia Zhang References: <20210124062907.88229-1-tianjia.zhang@linux.alibaba.com> <20210124062907.88229-4-tianjia.zhang@linux.alibaba.com> From: Tianjia Zhang Message-ID: <483f1ff9-9022-b7fc-5931-79c0c83f1289@linux.alibaba.com> Date: Tue, 16 Feb 2021 11:30:13 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/12/21 8:19 PM, Jarkko Sakkinen wrote: > On Thu, Feb 11, 2021 at 02:04:12PM +0800, Tianjia Zhang wrote: >> Hi, >> >> Sorry for the late reply. >> >> On 1/28/21 1:40 AM, Jarkko Sakkinen wrote: >>> I could bet some money that this does not bring any significant >>> performance gain. >>> >> >> Yes, this does not bring performance gains. This is not a change for >> performance, mainly to make the value of free_cnt look more accurate. >> >>> On Sun, Jan 24, 2021 at 02:29:05PM +0800, Tianjia Zhang wrote: >>>> `section->free_cnt` represents the free page in sgx_epc_section, >>>> which is assigned once after initialization. In fact, just after the >>>> initialization is completed, the pages are in the `init_laundry_list` >>>> list and cannot be allocated. This needs to be recovered by EREMOVE >>>> of function sgx_sanitize_section() before it can be used as a page >>>> that can be allocated. The sgx_sanitize_section() will be called in >>>> the kernel thread ksgxd. >>>> >>>> This patch moves the initialization of `section->free_cnt` from the >>>> initialization function `sgx_setup_epc_section()` to the function >>>> `sgx_sanitize_section()`, and then accumulates the count after the >>> >>> Use single quotes instead of hyphens. >>>>> successful execution of EREMOVE. This seems to be more reasonable, >>>> free_cnt will also truly reflect the allocatable free pages in EPC. >>>> >>>> Sined-off-by: Tianjia Zhang >>>> Reviewed-by: Sean Christopherson >>>> --- >>>> arch/x86/kernel/cpu/sgx/main.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c >>>> index 4465912174fd..e455ec7b3449 100644 >>>> --- a/arch/x86/kernel/cpu/sgx/main.c >>>> +++ b/arch/x86/kernel/cpu/sgx/main.c >>>> @@ -48,6 +48,7 @@ static void sgx_sanitize_section(struct sgx_epc_section *section) >>>> if (!ret) { >>>> spin_lock(§ion->lock); >>>> list_move(&page->list, §ion->page_list); >>>> + section->free_cnt++; >>>> spin_unlock(§ion->lock); >>> >>> Someone can try to allocate a page while sanitize process is in progress. >>> >>> I think it is better to keep critical sections in the form that when you >>> leave from one, the global state is legit. >>> >> >> Do you mean to move the critical section to protect the entire while loop? >> Of course, this is also possible, sanitize is a process only needed for >> initialization, and the possibility of conflict is very small. >> >> Best regards, >> Tianjia > > The big picture of this change to me, to be frank is that it's completely > useless. > > Please start with the picture. > > /Jarkko > I carefully considered your suggestion, and I will delete 2/5 and 3/5 in the next version. Best regards, Tianjia