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=-15.4 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 2844EC433DB for ; Thu, 11 Feb 2021 06:05:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F2B9164E87 for ; Thu, 11 Feb 2021 06:05:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229544AbhBKGFI (ORCPT ); Thu, 11 Feb 2021 01:05:08 -0500 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:51927 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229457AbhBKGE6 (ORCPT ); Thu, 11 Feb 2021 01:04:58 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R531e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=tianjia.zhang@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0UOPTk-a_1613023452; Received: from 30.27.210.10(mailfrom:tianjia.zhang@linux.alibaba.com fp:SMTPD_---0UOPTk-a_1613023452) by smtp.aliyun-inc.com(127.0.0.1); Thu, 11 Feb 2021 14:04:13 +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: Date: Thu, 11 Feb 2021 14:04:12 +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 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