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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A72C3C77B61 for ; Mon, 10 Apr 2023 18:16:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229718AbjDJSQU (ORCPT ); Mon, 10 Apr 2023 14:16:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229649AbjDJSQS (ORCPT ); Mon, 10 Apr 2023 14:16:18 -0400 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AD1F91BEB; Mon, 10 Apr 2023 11:16:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1681150577; x=1712686577; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=0ix6Ckdt+5OCc4ou2uz+XeRPoBdpCTfcvuC4e0JJtKY=; b=I9u49lSrUF+aCtXmGpkGJT0EInLdutiuhCs7fip5M3E0e4Rgi7JRbmaP HKnVhlJYR2Po0my1YMZilpcvaIeTOYPINRjKs4ciIwAnBFUm81336HTWD 08oUzZRlwfgmDIOF/aniQ+v7AWNB/DDfq/58rKTtByegjg84HDU1Fhs9P mJwO+kQ+VogxKHDSjPa6aZD3mzOcoCEVwu6b/6KF8a60EygMB5kMPEQnd aQqv+EHaKjh/k6chW08USkrqMvQEkClmH79G17/j0O34pYzuhXNpCLhKm gcmoJOs4RuTKJr/OncKAUN/vDT3H4Ysit1ezoYZv/fYtNoZshG3Ek1EyB w==; X-IronPort-AV: E=McAfee;i="6600,9927,10676"; a="327516577" X-IronPort-AV: E=Sophos;i="5.98,333,1673942400"; d="scan'208";a="327516577" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Apr 2023 11:16:17 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10676"; a="752850815" X-IronPort-AV: E=Sophos;i="5.98,333,1673942400"; d="scan'208";a="752850815" Received: from arsetion-mobl.amr.corp.intel.com (HELO [10.209.122.228]) ([10.209.122.228]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Apr 2023 11:16:16 -0700 Message-ID: Date: Mon, 10 Apr 2023 11:16:15 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH v7 23/33] x86/fred: let ret_from_fork() jmp to fred_exit_user when FRED is enabled Content-Language: en-US To: Xin Li , linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, peterz@infradead.org, andrew.cooper3@citrix.com, seanjc@google.com, pbonzini@redhat.com, ravi.v.shankar@intel.com, jiangshanlai@gmail.com, shan.kang@intel.com References: <20230404102716.1795-1-xin3.li@intel.com> <20230404102716.1795-24-xin3.li@intel.com> From: Dave Hansen In-Reply-To: <20230404102716.1795-24-xin3.li@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/4/23 03:27, Xin Li wrote: > --- a/arch/x86/entry/entry_64.S > +++ b/arch/x86/entry/entry_64.S > @@ -299,7 +299,12 @@ SYM_CODE_START_NOALIGN(ret_from_fork) > UNWIND_HINT_REGS > movq %rsp, %rdi > call syscall_exit_to_user_mode /* returns with IRQs disabled */ > +#ifdef CONFIG_X86_FRED > + ALTERNATIVE "jmp swapgs_restore_regs_and_return_to_usermode", \ > + "jmp fred_exit_user", X86_FEATURE_FRED > +#else > jmp swapgs_restore_regs_and_return_to_usermode > +#endif Does the #ifdef really buy us anything here? I guess it might save a *TINY* amount of time at alternative processing time. But that doesn't really seem worth it.