From patchwork Tue Aug 1 08:32:43 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: "Li, Xin3" X-Patchwork-Id: 13335936 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 lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BA13AC04FE0 for ; Tue, 1 Aug 2023 09:02:15 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.573844.898823 (Exim 4.92) (envelope-from ) id 1qQlGW-0005ob-Eq; Tue, 01 Aug 2023 09:02:04 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 573844.898823; Tue, 01 Aug 2023 09:02:04 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1qQlGW-0005m6-6s; Tue, 01 Aug 2023 09:02:04 +0000 Received: by outflank-mailman (input) for mailman id 573844; Tue, 01 Aug 2023 09:02:03 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1qQlGV-0005E5-8R for xen-devel@lists.xenproject.org; Tue, 01 Aug 2023 09:02:03 +0000 Received: from mgamail.intel.com (unknown [134.134.136.31]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 10edf405-304a-11ee-8613-37d641c3527e; Tue, 01 Aug 2023 11:01:59 +0200 (CEST) Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Aug 2023 02:01:52 -0700 Received: from unknown (HELO fred..) ([172.25.112.68]) by fmsmga006.fm.intel.com with ESMTP; 01 Aug 2023 02:01:51 -0700 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 10edf405-304a-11ee-8613-37d641c3527e DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1690880519; x=1722416519; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=6FF6EgUyznIqvHXwn5+F1gytlgvayKLTt5Pzm0+v43k=; b=QuNFywc+UMpHpIbFImf6ilSe8NIVmH1wzA3OfKAbyCAgOCnK4yNVgbxP WP3icBVaReSFeX+TcvWMi6+ApwJpI0EG1BB29A1S13ci12RnBilxcwsMl Gac6bI282B8Yv04G9dy0/pFUFAazorgz4Sc/GMKThN2tB7Dyp7sfBpNyB oqCccw6NkiUiizzpXL4dav6CeRulDABlBNihElIfyAKCp9c9Hn9Bc2blw BlYzHetUuPZUefWQevdwTKlJ62iTyydpgQ18veiZi53NE7+NjHClGR5Hw 8fu72evGTMXeaKUWiZFEX29klZ23l1jAWiBYB58cHqOnsDuw1NfY7o2fB g==; X-IronPort-AV: E=McAfee;i="6600,9927,10788"; a="433082066" X-IronPort-AV: E=Sophos;i="6.01,246,1684825200"; d="scan'208";a="433082066" X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10788"; a="975216947" X-IronPort-AV: E=Sophos;i="6.01,246,1684825200"; d="scan'208";a="975216947" From: Xin Li To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org, linux-hyperv@vger.kernel.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org Cc: Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , Andy Lutomirski , Oleg Nesterov , Tony Luck , "K . Y . Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Sean Christopherson , Peter Zijlstra , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Josh Poimboeuf , "Paul E . McKenney" , Catalin Marinas , Randy Dunlap , Steven Rostedt , Kim Phillips , Xin Li , Hyeonggon Yoo <42.hyeyoo@gmail.com>, "Liam R . Howlett" , Sebastian Reichel , "Kirill A . Shutemov" , Suren Baghdasaryan , Pawan Gupta , Babu Moger , Jim Mattson , Sandipan Das , Lai Jiangshan , Hans de Goede , Reinette Chatre , Daniel Sneddon , Breno Leitao , Nikunj A Dadhania , Brian Gerst , Sami Tolvanen , Alexander Potapenko , Andrew Morton , Arnd Bergmann , "Eric W . Biederman" , Kees Cook , Masami Hiramatsu , Masahiro Yamada , Ze Gao , Fei Li , Conghui , Ashok Raj , "Jason A . Donenfeld" , Mark Rutland , Jacob Pan , Jiapeng Chong , Jane Malalane , David Woodhouse , Boris Ostrovsky , Arnaldo Carvalho de Melo , Yantengsi , Christophe Leroy , Sathvika Vasireddy Subject: [PATCH RESEND v9 01/36] Documentation/x86/64: Add documentation for FRED Date: Tue, 1 Aug 2023 01:32:43 -0700 Message-Id: <20230801083318.8363-2-xin3.li@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230801083318.8363-1-xin3.li@intel.com> References: <20230801083318.8363-1-xin3.li@intel.com> MIME-Version: 1.0 Briefly introduce FRED, its advantages compared to IDT, and its Linux enabling. Signed-off-by: Xin Li --- Documentation/arch/x86/x86_64/fred.rst | 102 ++++++++++++++++++++++++ Documentation/arch/x86/x86_64/index.rst | 1 + 2 files changed, 103 insertions(+) create mode 100644 Documentation/arch/x86/x86_64/fred.rst diff --git a/Documentation/arch/x86/x86_64/fred.rst b/Documentation/arch/x86/x86_64/fred.rst new file mode 100644 index 000000000000..27c980e882ba --- /dev/null +++ b/Documentation/arch/x86/x86_64/fred.rst @@ -0,0 +1,102 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================================= +Flexible Return and Event Delivery (FRED) +========================================= + +Overview +======== + +The FRED architecture defines simple new transitions that change +privilege level (ring transitions). The FRED architecture was +designed with the following goals: + +1) Improve overall performance and response time by replacing event + delivery through the interrupt descriptor table (IDT event + delivery) and event return by the IRET instruction with lower + latency transitions. + +2) Improve software robustness by ensuring that event delivery + establishes the full supervisor context and that event return + establishes the full user context. + +The new transitions defined by the FRED architecture are FRED event +delivery and, for returning from events, two FRED return instructions. +FRED event delivery can effect a transition from ring 3 to ring 0, but +it is used also to deliver events incident to ring 0. One FRED +instruction (ERETU) effects a return from ring 0 to ring 3, while the +other (ERETS) returns while remaining in ring 0. Collectively, FRED +event delivery and the FRED return instructions are FRED transitions. + +In addition to these transitions, the FRED architecture defines a new +instruction (LKGS) for managing the state of the GS segment register. +The LKGS instruction can be used by 64-bit operating systems that do +not use the new FRED transitions. + +Software based event dispatching +================================ + +FRED operates differently from IDT in terms of event handling. Instead +of directly dispatching an event to its handler based on the event +vector, FRED requires the software to dispatch an event to its handler +based on both the event's type and vector. Therefore, an event +dispatch framework must be implemented to facilitate the +event-to-handler dispatch process. The FRED event dispatch framework +assumes control once an event is delivered, starting from two FRED +entry points, after which several event dispatch tables are introduced +to facilitate the dispatching. + +The first level dispatching is event type based, and two tables need +to be defined, one for ring 3 event dispatching, and the other +for ring 0. + +The second level dispatching is event vector based, and +several tables need to be defined, e.g., an exception handler table +for exception dispatching. + +Full supervisor/user context +============================ + +FRED event delivery atomically save and restore full supervisor/user +context upon event delivery and return. Thus it avoids the problem of +transient states due to %cr2 and/or %dr6, thus it is no longer needed +to handle all the ugly corner cases caused by half baked CPU states. + +FRED allows explicit unblock of NMI with new event return instructions +ERETS/ERETU, avoiding the mess caused by IRET which unconditionally +unblocks NMI, when an exception happens during NMI handling. + +FRED always restores the full value of %rsp, thus ESPFIX is no longer +needed when FRED is enabled. + +LKGS +==== + +LKGS behaves like the MOV to GS instruction except that it loads the +base address into the IA32_KERNEL_GS_BASE MSR instead of the GS +segment’s descriptor cache, which is exactly what Linux kernel does +to load user level GS base. With LKGS, it ends up with avoiding +mucking with kernel GS. + +Because FRED event delivery from ring 3 swaps the value of the GS base +address and that of the IA32_KERNEL_GS_BASE MSR, and ERETU swaps the +value of the GS base address and that of the IA32_KERNEL_GS_BASE MSR, +plus the introduction of LKGS instruction, the SWAPGS instruction is +no longer needed when FRED is enabled, thus is disallowed (#UD). + +Stack levels +============ + +4 stack levels 0~3 are introduced to replace the un-reentrant IST for +handling events. Each stack level could be configured to use a +dedicated stack. + +The current stack level could be unchanged or go higher upon FRED +event delivery. If unchanged, the CPU keeps using the current event +stack. If higher, the CPU switches to a new stack specified by the +stack MSR of the new stack level. + +Only execution of a FRED return instruction ERETU or ERETS could lower +the current stack level, causing the CPU to switch back to the stack +it was on before a previous event delivery. +satck. diff --git a/Documentation/arch/x86/x86_64/index.rst b/Documentation/arch/x86/x86_64/index.rst index a56070fc8e77..ad15e9bd623f 100644 --- a/Documentation/arch/x86/x86_64/index.rst +++ b/Documentation/arch/x86/x86_64/index.rst @@ -15,3 +15,4 @@ x86_64 Support cpu-hotplug-spec machinecheck fsgs + fred