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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B75B9C433EF for ; Thu, 7 Oct 2021 17:31:52 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 30DE460E09 for ; Thu, 7 Oct 2021 17:31:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 30DE460E09 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:52270 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mYXFH-0002GT-8z for qemu-devel@archiver.kernel.org; Thu, 07 Oct 2021 13:31:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60918) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYX6X-0001GD-FO for qemu-devel@nongnu.org; Thu, 07 Oct 2021 13:22:49 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:46290) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYX6S-0001Lb-O4 for qemu-devel@nongnu.org; Thu, 07 Oct 2021 13:22:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633627362; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=y2c+YGN6wU3B+050Do8UhDaOlKhi7UqTcLqGXK6cv28=; b=fBUusiZbIWtkEzOu8TawoH+VY94wygJjbDR3W9Fg79gyP8IhKGVOlfNT0MxoHl8ZnxrYVt vonqdLwbuFcax+As0sLJAzGsq8oZ36gohzwhdg/4+QCMNltmExomsFa5FbzQSwAIYt64FJ Uh0m9OUMO/ArUp9UAG4n5g9VlmOMEvo= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-441-Wov9Vw4ePaq7_hELgIXEwg-1; Thu, 07 Oct 2021 13:22:38 -0400 X-MC-Unique: Wov9Vw4ePaq7_hELgIXEwg-1 Received: by mail-wr1-f69.google.com with SMTP id p12-20020adfc38c000000b00160d6a7e293so2767355wrf.18 for ; Thu, 07 Oct 2021 10:22:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=y2c+YGN6wU3B+050Do8UhDaOlKhi7UqTcLqGXK6cv28=; b=3MXd+ESdkk3liirH+kRaBQMfvr78JBPcep3otQ3jW2B1Bu6i65d4iB3Km5dlo6Ebgp CdU7pQz0HIGK7wVfXBkol97/zhtLz4YU6inHdQjXZ/HT5IVei8CVXLvgXVbvlOrhnfPt AHQhiilrX4gJ+MPngmXN09606WxS0WimDHOtdSO2tCq6tGOoHtHH0vZ54MNikcr6M9uZ PouhF7mQIn4mLrD8KeL3PjgPbzLkkjAAHSJn7/eveEPkRUT8LGsaX40L/rpoPkXL4F1J TRPfYWZDBSSvkahsAXmHLkfltxxJ6mwaoDuuh99sub3vPbhN3dAAqcg/eMKVJTUTtab+ pV3w== X-Gm-Message-State: AOAM530lYSr72cVebnq4W3/TIRuo416k1D4D3kxtv2UyIXONtk5/ctRf DzuljyfY3O36y588UzHjWpILJxgNeAAdi50IqrCIeJfvR9SmBeBjCPDuy569OOpQZRVZIFvdo5D NCm0nggFNMXHtGu0= X-Received: by 2002:a1c:9892:: with SMTP id a140mr5988968wme.187.1633627357403; Thu, 07 Oct 2021 10:22:37 -0700 (PDT) X-Google-Smtp-Source: ABdhPJy3Y9mAKHjCv2YKJWmeW2zQEasbnHiNok9T+WfiQrpReSdPvc4ydF10Uql1MwWxw6bYFDjz3A== X-Received: by 2002:a1c:9892:: with SMTP id a140mr5988927wme.187.1633627357125; Thu, 07 Oct 2021 10:22:37 -0700 (PDT) Received: from work-vm (cpc109025-salf6-2-0-cust480.10-2.cable.virginm.net. [82.30.61.225]) by smtp.gmail.com with ESMTPSA id h17sm229723wrx.55.2021.10.07.10.22.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 Oct 2021 10:22:36 -0700 (PDT) Date: Thu, 7 Oct 2021 18:22:34 +0100 From: "Dr. David Alan Gilbert" To: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Subject: Re: [PATCH v4 16/23] target/i386/sev: Remove stubs by using code elision Message-ID: References: <20211007161716.453984-1-philmd@redhat.com> <20211007161716.453984-17-philmd@redhat.com> <6080fa16-66aa-570e-93c8-09be2ced9431@redhat.com> MIME-Version: 1.0 In-Reply-To: <6080fa16-66aa-570e-93c8-09be2ced9431@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.05, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Daniel P . Berrange" , Eduardo Habkost , kvm@vger.kernel.org, "Michael S. Tsirkin" , Sergio Lopez , James Bottomley , Richard Henderson , qemu-devel@nongnu.org, Dov Murik , Brijesh Singh , Paolo Bonzini , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Philippe Mathieu-Daudé (philmd@redhat.com) wrote: > On 10/7/21 19:07, Dr. David Alan Gilbert wrote: > > * Philippe Mathieu-Daudé (philmd@redhat.com) wrote: > >> Only declare sev_enabled() and sev_es_enabled() when CONFIG_SEV is > >> set, to allow the compiler to elide unused code. Remove unnecessary > >> stubs. > >> > >> Signed-off-by: Philippe Mathieu-Daudé > > > > What makes it allowed to *rely* on the compiler eliding calls? > > I am not aware of a particular requirement on the compiler for code > elision, however we already use this syntax: > > $ git grep -A4 'ifdef CONFIG_' include/sysemu/ > ... > include/sysemu/tcg.h:11:#ifdef CONFIG_TCG > include/sysemu/tcg.h-12-extern bool tcg_allowed; > include/sysemu/tcg.h-13-#define tcg_enabled() (tcg_allowed) > include/sysemu/tcg.h-14-#else > include/sysemu/tcg.h-15-#define tcg_enabled() 0 So that I'm fine with, the bit I'm more worried about is the bit where inside the if () we call functions (like sev_get_cbit_position ) which we know the compiler will elide; I'm sure any sane compiler will, but..... Looking at your example, in cpu.c there's still places that ifdef around areas with tcg_enabled. Dave > ... > > Cc'ing Richard/Eric/Daniel who have more experience with compiler > features in case they can enlighten me here. > > >> --- > >> target/i386/sev.h | 14 ++++++++++++-- > >> target/i386/cpu.c | 13 +++++++------ > >> target/i386/sev-stub.c | 41 ----------------------------------------- > >> target/i386/meson.build | 2 +- > >> 4 files changed, 20 insertions(+), 50 deletions(-) > >> delete mode 100644 target/i386/sev-stub.c > >> > >> diff --git a/target/i386/sev.h b/target/i386/sev.h > >> index c96072bf78d..d9548e3e642 100644 > >> --- a/target/i386/sev.h > >> +++ b/target/i386/sev.h > >> @@ -14,6 +14,10 @@ > >> #ifndef QEMU_SEV_I386_H > >> #define QEMU_SEV_I386_H > >> > >> +#ifndef CONFIG_USER_ONLY > >> +#include CONFIG_DEVICES /* CONFIG_SEV */ > >> +#endif > >> + > >> #include "exec/confidential-guest-support.h" > >> #include "qapi/qapi-types-misc-target.h" > >> > >> @@ -35,8 +39,14 @@ typedef struct SevKernelLoaderContext { > >> size_t cmdline_size; > >> } SevKernelLoaderContext; > >> > >> -bool sev_enabled(void); > >> -extern bool sev_es_enabled(void); > >> +#ifdef CONFIG_SEV > >> + bool sev_enabled(void); > >> +bool sev_es_enabled(void); > >> +#else > >> +#define sev_enabled() 0 > >> +#define sev_es_enabled() 0 > >> +#endif > >> + > >> extern SevInfo *sev_get_info(void); > >> extern uint32_t sev_get_cbit_position(void); > >> extern uint32_t sev_get_reduced_phys_bits(void); > >> diff --git a/target/i386/cpu.c b/target/i386/cpu.c > >> index 8289dc87bd5..fc3ed80ef1e 100644 > >> --- a/target/i386/cpu.c > >> +++ b/target/i386/cpu.c > >> @@ -5764,12 +5764,13 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, > >> *edx = 0; > >> break; > >> case 0x8000001F: > >> - *eax = sev_enabled() ? 0x2 : 0; > >> - *eax |= sev_es_enabled() ? 0x8 : 0; > >> - *ebx = sev_get_cbit_position(); > >> - *ebx |= sev_get_reduced_phys_bits() << 6; > >> - *ecx = 0; > >> - *edx = 0; > >> + *eax = *ebx = *ecx = *edx = 0; > >> + if (sev_enabled()) { > >> + *eax = 0x2; > >> + *eax |= sev_es_enabled() ? 0x8 : 0; > >> + *ebx = sev_get_cbit_position(); > >> + *ebx |= sev_get_reduced_phys_bits() << 6; > >> + } > >> break; > >> default: > >> /* reserved values: zero */ > >> diff --git a/target/i386/sev-stub.c b/target/i386/sev-stub.c > >> deleted file mode 100644 > >> index 7e8b6f9a259..00000000000 > >> --- a/target/i386/sev-stub.c > >> +++ /dev/null > >> @@ -1,41 +0,0 @@ > >> -/* > >> - * QEMU SEV stub > >> - * > >> - * Copyright Advanced Micro Devices 2018 > >> - * > >> - * Authors: > >> - * Brijesh Singh > >> - * > >> - * This work is licensed under the terms of the GNU GPL, version 2 or later. > >> - * See the COPYING file in the top-level directory. > >> - * > >> - */ > >> - > >> -#include "qemu/osdep.h" > >> -#include "qapi/error.h" > >> -#include "sev.h" > >> - > >> -bool sev_enabled(void) > >> -{ > >> - return false; > >> -} > >> - > >> -uint32_t sev_get_cbit_position(void) > >> -{ > >> - return 0; > >> -} > >> - > >> -uint32_t sev_get_reduced_phys_bits(void) > >> -{ > >> - return 0; > >> -} > >> - > >> -bool sev_es_enabled(void) > >> -{ > >> - return false; > >> -} > >> - > >> -bool sev_add_kernel_loader_hashes(SevKernelLoaderContext *ctx, Error **errp) > >> -{ > >> - g_assert_not_reached(); > >> -} > >> diff --git a/target/i386/meson.build b/target/i386/meson.build > >> index a4f45c3ec1d..ae38dc95635 100644 > >> --- a/target/i386/meson.build > >> +++ b/target/i386/meson.build > >> @@ -6,7 +6,7 @@ > >> 'xsave_helper.c', > >> 'cpu-dump.c', > >> )) > >> -i386_ss.add(when: 'CONFIG_SEV', if_true: files('host-cpu.c'), if_false: files('sev-stub.c')) > >> +i386_ss.add(when: 'CONFIG_SEV', if_true: files('host-cpu.c')) > >> > >> # x86 cpu type > >> i386_ss.add(when: 'CONFIG_KVM', if_true: files('host-cpu.c')) > >> -- > >> 2.31.1 > >> > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK