From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x2255SH2OrxE299kDv+xy3DUixAAbKGy9eEukAWfvUmPBc7iXM2vvNtdV/wq09gHMDv2/Aa7Y ARC-Seal: i=1; a=rsa-sha256; t=1517250879; cv=none; d=google.com; s=arc-20160816; b=MKvRhHgEHq4mItJAVSyerqOyqXJp9y9JT4KjcKdyTjl4qPnB46QKVUnkY+FRdLeF5M kdJGq3H8Pah1ZiGBfRswgt+w1MrAQPuUyWYq0fuQVcgTcX0MTHLCeQ7bFIaWEFrb9Qvg cFmRiwTTexl2JfB29xeb52A47pw+3H2Dj/5D4vZpHxbm8jW00wotayEPrRtOA3AZ/pGW b3DJLaV40hEx1KJl9prIsgpiirM2hXFx8vgq2EFaUNHBCsxSVEOMU8YnIpxSmSTWwBI3 kEzFMoDM0F9Z4/TgXRzfaSojAf/txFtxsNzVElCw7sjbA9g59hsnRVEmEpi37rBp7f3L HSuQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:content-transfer-encoding :content-language:in-reply-to:mime-version:user-agent:date :message-id:from:references:cc:to:subject:arc-authentication-results; bh=DiNa3Ksg8ZxM7CUdZo2bc6+aMljo9TLceDr04kSXe8o=; b=smQPuGqv6nMwTAhXfxzZK36X2Ib0H6R8fNMf5N8OxsK8shuMalblMqyr3yF9m8TBIK 33GxPvv/18kMPyOpjNu1Qb5TKSmXbp5Bk6V3kqTkMhHYSGDfuf0PpQMIwV5dzrA6Wx0C pDjLXc0hR0Xv+R1jS4BKbN0b+GuQuxbevT9TP1zYtN2rnwUsEPCrl5xTdU5qzpkxYdcW /1fHedUIw4Y5cTH2jLybq1rgTn8TTW1fpJEH2yVO1DSHCnYJNhdl+SKZyWQTLOnRmYDB 5NlxWAC7yGw4UHGktylG4r8twX2elgCS+jLWe8TCrbHA1XZTfvy0Lq6d6QXxTmg8L9n3 aCYw== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kselftest-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kselftest-owner@vger.kernel.org Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kselftest-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kselftest-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751357AbeA2Sej (ORCPT ); Mon, 29 Jan 2018 13:34:39 -0500 Received: from terminus.zytor.com ([65.50.211.136]:60583 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751301AbeA2Sej (ORCPT ); Mon, 29 Jan 2018 13:34:39 -0500 Subject: Re: selftests/x86/fsgsbase_64 test problem To: Andy Lutomirski Cc: Andy Lutomirski , Borislav Petkov , Dan Rue , Shuah Khan , Ingo Molnar , Dmitry Safonov , "open list:KERNEL SELFTEST FRAMEWORK" , LKML References: <20180126153631.ha7yc33fj5uhitjo@xps> <46328204-e363-e517-f30c-c8c94ac1442c@zytor.com> <624b9e67-14ee-6882-e55e-f337ec2471d3@zytor.com> From: "H. Peter Anvin" Message-ID: <0b0a3cea-d951-d3be-16de-a0e9d50cb2ba@zytor.com> Date: Mon, 29 Jan 2018 10:30:05 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kselftest-owner@vger.kernel.org X-Mailing-List: linux-kselftest@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590669876861238825?= X-GMAIL-MSGID: =?utf-8?q?1590952858424512164?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 01/29/18 10:26, Andy Lutomirski wrote: >>> >>> That will utterly suck on non-UMIP machines that have >>> hypervisor-provided UMIP emulation. >> >> Is that a valid thing to optimize for, especially given that paranoid >> entries aren't the most common anyway? > > A bunch of people seem to care about NMI performance for perf. > That wasn't really the question... > And the current patch set works without this trick. But I believe the tricks it uses are fragile. > FWIW, if we switch all entries to the entry text trampoline, we get direct percpu access for free. That might be a better option. -hpa