From patchwork Mon Mar 6 14:14:01 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Huang, Kai" X-Patchwork-Id: 13161268 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 419BAC61DA4 for ; Mon, 6 Mar 2023 14:22:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230284AbjCFOWL (ORCPT ); Mon, 6 Mar 2023 09:22:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230383AbjCFOVk (ORCPT ); Mon, 6 Mar 2023 09:21:40 -0500 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45C9534C1A; Mon, 6 Mar 2023 06:20:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1678112417; x=1709648417; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=coSckihc/FGLGVwvcV+LqtmdmdjmpY1DZ81B3xj/jnI=; b=BOvMfZGQ22a0knNNEINtKfNaNHAq3eF5Gvo2PrnWtslnzGqYMyAbYNXP GshE2izvL+NvKzPFKGphqQZLWnzO3A79e1pwangwCVmn0zzTfdwSBA+zc gXl4UXgJJA+Jx+Jiseut1kloC6DEtEPbAcyWd5fjq/kJv69y2gFLeVUyr PrmRW01aM6uFaMt8dZPo/dIxnmA5gyqcxbu2dIfSODsdciH8rns9nAaee 3+06uMzASgTG6tXm6j3HaqSHGLjiFR2DKN0GcuYzEhZUjPqq92/3MY162 WBVTDC7PA4oJefCfqdTY4A3eRL0pya4RTnIg7qKFifJt3vFW+WVM0gO+f Q==; X-IronPort-AV: E=McAfee;i="6500,9779,10641"; a="337080359" X-IronPort-AV: E=Sophos;i="5.98,238,1673942400"; d="scan'208";a="337080359" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Mar 2023 06:15:47 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10641"; a="765232577" X-IronPort-AV: E=Sophos;i="5.98,238,1673942400"; d="scan'208";a="765232577" Received: from jwhisle1-mobl2.amr.corp.intel.com (HELO khuang2-desk.gar.corp.intel.com) ([10.212.92.57]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Mar 2023 06:15:43 -0800 From: Kai Huang To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: linux-mm@kvack.org, dave.hansen@intel.com, peterz@infradead.org, tglx@linutronix.de, seanjc@google.com, pbonzini@redhat.com, dan.j.williams@intel.com, rafael.j.wysocki@intel.com, kirill.shutemov@linux.intel.com, ying.huang@intel.com, reinette.chatre@intel.com, len.brown@intel.com, tony.luck@intel.com, ak@linux.intel.com, isaku.yamahata@intel.com, chao.gao@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, david@redhat.com, bagasdotme@gmail.com, sagis@google.com, imammedo@redhat.com, kai.huang@intel.com Subject: [PATCH v10 16/16] Documentation/x86: Add documentation for TDX host support Date: Tue, 7 Mar 2023 03:14:01 +1300 Message-Id: X-Mailer: git-send-email 2.39.2 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Add documentation for TDX host kernel support. There is already one file Documentation/x86/tdx.rst containing documentation for TDX guest internals. Also reuse it for TDX host kernel support. Introduce a new level menu "TDX Guest Support" and move existing materials under it, and add a new menu for TDX host kernel support. Signed-off-by: Kai Huang --- Documentation/x86/tdx.rst | 186 +++++++++++++++++++++++++++++++++++--- 1 file changed, 175 insertions(+), 11 deletions(-) diff --git a/Documentation/x86/tdx.rst b/Documentation/x86/tdx.rst index dc8d9fd2c3f7..a6f66a28bef4 100644 --- a/Documentation/x86/tdx.rst +++ b/Documentation/x86/tdx.rst @@ -10,6 +10,170 @@ encrypting the guest memory. In TDX, a special module running in a special mode sits between the host and the guest and manages the guest/host separation. +TDX Host Kernel Support +======================= + +TDX introduces a new CPU mode called Secure Arbitration Mode (SEAM) and +a new isolated range pointed by the SEAM Ranger Register (SEAMRR). A +CPU-attested software module called 'the TDX module' runs inside the new +isolated range to provide the functionalities to manage and run protected +VMs. + +TDX also leverages Intel Multi-Key Total Memory Encryption (MKTME) to +provide crypto-protection to the VMs. TDX reserves part of MKTME KeyIDs +as TDX private KeyIDs, which are only accessible within the SEAM mode. +BIOS is responsible for partitioning legacy MKTME KeyIDs and TDX KeyIDs. + +Before the TDX module can be used to create and run protected VMs, it +must be loaded into the isolated range and properly initialized. The TDX +architecture doesn't require the BIOS to load the TDX module, but the +kernel assumes it is loaded by the BIOS. + +TDX boot-time detection +----------------------- + +The kernel detects TDX by detecting TDX private KeyIDs during kernel +boot. Below dmesg shows when TDX is enabled by BIOS:: + + [..] tdx: BIOS enabled: private KeyID range: [16, 64). + +TDX module detection and initialization +--------------------------------------- + +There is no CPUID or MSR to detect the TDX module. The kernel detects it +by initializing it. + +The kernel talks to the TDX module via the new SEAMCALL instruction. The +TDX module implements SEAMCALL leaf functions to allow the kernel to +initialize it. + +Initializing the TDX module consumes roughly ~1/256th system RAM size to +use it as 'metadata' for the TDX memory. It also takes additional CPU +time to initialize those metadata along with the TDX module itself. Both +are not trivial. The kernel initializes the TDX module at runtime on +demand. + +Besides initializing the TDX module, a per-cpu initialization SEAMCALL +must be done on one cpu before any other SEAMCALLs can be made on that +cpu. + +The kernel provides two functions, tdx_enable() and tdx_cpu_enable() to +allow the user of TDX to enable the TDX module and enable TDX on local +cpu. + +Making SEAMCALL requires the CPU already being in VMX operation (VMXON +has been done). For now both tdx_enable() and tdx_cpu_enable() don't +handle VMXON internally, but depends on the caller to guarantee that. + +To enable TDX, the user of TDX should: 1) hold read lock of CPU hotplug +lock; 2) do VMXON and tdx_enable_cpu() on all online cpus successfully; +3) call tdx_enable(). For example:: + + cpus_read_lock(); + on_each_cpu(vmxon_and_tdx_cpu_enable()); + ret = tdx_enable(); + cpus_read_unlock(); + if (ret) + goto no_tdx; + // TDX is ready to use + +And the user of TDX must be guarantee tdx_cpu_enable() has beene +successfully done on any cpu before it wants to run any other SEAMCALL. +A typical usage is do both VMXON and tdx_cpu_enable() in CPU hotplug +online callback, and refuse to online if tdx_cpu_enable() fails. + +User can consult dmesg to see the presence of the TDX module, and whether +it has been initialized. + +If the TDX module is not loaded, dmesg shows below:: + + [..] tdx: TDX module is not loaded. + +If the TDX module is initialized successfully, dmesg shows something +like below:: + + [..] tdx: TDX module: attributes 0x0, vendor_id 0x8086, major_version 1, minor_version 0, build_date 20211209, build_num 160 + [..] tdx: 262668 KBs allocated for PAMT. + [..] tdx: TDX module initialized. + +If the TDX module failed to initialize, dmesg also shows it failed to +initialize:: + + [..] tdx: TDX module initialization failed ... + +TDX Interaction to Other Kernel Components +------------------------------------------ + +TDX Memory Policy +~~~~~~~~~~~~~~~~~ + +TDX reports a list of "Convertible Memory Region" (CMR) to tell the +kernel which memory is TDX compatible. The kernel needs to build a list +of memory regions (out of CMRs) as "TDX-usable" memory and pass those +regions to the TDX module. Once this is done, those "TDX-usable" memory +regions are fixed during module's lifetime. + +To keep things simple, currently the kernel simply guarantees all pages +in the page allocator are TDX memory. Specifically, the kernel uses all +system memory in the core-mm at the time of initializing the TDX module +as TDX memory, and in the meantime, refuses to online any non-TDX-memory +in the memory hotplug. + +This can be enhanced in the future, i.e. by allowing adding non-TDX +memory to a separate NUMA node. In this case, the "TDX-capable" nodes +and the "non-TDX-capable" nodes can co-exist, but the kernel/userspace +needs to guarantee memory pages for TDX guests are always allocated from +the "TDX-capable" nodes. + +Physical Memory Hotplug +~~~~~~~~~~~~~~~~~~~~~~~ + +Note TDX assumes convertible memory is always physically present during +machine's runtime. A non-buggy BIOS should never support hot-removal of +any convertible memory. This implementation doesn't handle ACPI memory +removal but depends on the BIOS to behave correctly. + +CPU Hotplug +~~~~~~~~~~~ + +TDX module requires the per-cpu initialization SEAMCALL (TDH.SYS.LP.INIT) +must be done on one cpu before any other SEAMCALLs can be made on that +cpu, including those involved during the module initialization. + +The kernel provides tdx_cpu_enable() to let the user of TDX to do it when +the user wants to use a new cpu for TDX task. + +TDX doesn't support physical (ACPI) CPU hotplug. During machine boot, +TDX verifies all boot-time present logical CPUs are TDX compatible before +enabling TDX. A non-buggy BIOS should never support hot-add/removal of +physical CPU. Currently the kernel doesn't handle physical CPU hotplug, +but depends on the BIOS to behave correctly. + +Note TDX works with CPU logical online/offline, thus the kernel still +allows to offline logical CPU and online it again. + +Kexec() +~~~~~~~ + +There are two problems in terms of using kexec() to boot to a new kernel +when the old kernel has enabled TDX: 1) Part of the memory pages are +still TDX private pages; 2) There might be dirty cachelines associated +with TDX private pages. + +The first problem doesn't matter. KeyID 0 doesn't have integrity check. +Even the new kernel wants use any non-zero KeyID, it needs to convert +the memory to that KeyID and such conversion would work from any KeyID. + +However the old kernel needs to guarantee there's no dirty cacheline +left behind before booting to the new kernel to avoid silent corruption +from later cacheline writeback (Intel hardware doesn't guarantee cache +coherency across different KeyIDs). + +Similar to AMD SME, the kernel just uses wbinvd() to flush cache before +booting to the new kernel. + +TDX Guest Support +================= Since the host cannot directly access guest registers or memory, much normal functionality of a hypervisor must be moved into the guest. This is implemented using a Virtualization Exception (#VE) that is handled by the @@ -20,7 +184,7 @@ TDX includes new hypercall-like mechanisms for communicating from the guest to the hypervisor or the TDX module. New TDX Exceptions -================== +------------------ TDX guests behave differently from bare-metal and traditional VMX guests. In TDX guests, otherwise normal instructions or memory accesses can cause @@ -30,7 +194,7 @@ Instructions marked with an '*' conditionally cause exceptions. The details for these instructions are discussed below. Instruction-based #VE ---------------------- +~~~~~~~~~~~~~~~~~~~~~ - Port I/O (INS, OUTS, IN, OUT) - HLT @@ -41,7 +205,7 @@ Instruction-based #VE - CPUID* Instruction-based #GP ---------------------- +~~~~~~~~~~~~~~~~~~~~~ - All VMX instructions: INVEPT, INVVPID, VMCLEAR, VMFUNC, VMLAUNCH, VMPTRLD, VMPTRST, VMREAD, VMRESUME, VMWRITE, VMXOFF, VMXON @@ -52,7 +216,7 @@ Instruction-based #GP - RDMSR*,WRMSR* RDMSR/WRMSR Behavior --------------------- +~~~~~~~~~~~~~~~~~~~~ MSR access behavior falls into three categories: @@ -73,7 +237,7 @@ trapping and handling in the TDX module. Other than possibly being slow, these MSRs appear to function just as they would on bare metal. CPUID Behavior --------------- +~~~~~~~~~~~~~~ For some CPUID leaves and sub-leaves, the virtualized bit fields of CPUID return values (in guest EAX/EBX/ECX/EDX) are configurable by the @@ -93,7 +257,7 @@ not know how to handle. The guest kernel may ask the hypervisor for the value with a hypercall. #VE on Memory Accesses -====================== +---------------------- There are essentially two classes of TDX memory: private and shared. Private memory receives full TDX protections. Its content is protected @@ -107,7 +271,7 @@ entries. This helps ensure that a guest does not place sensitive information in shared memory, exposing it to the untrusted hypervisor. #VE on Shared Memory --------------------- +~~~~~~~~~~~~~~~~~~~~ Access to shared mappings can cause a #VE. The hypervisor ultimately controls whether a shared memory access causes a #VE, so the guest must be @@ -127,7 +291,7 @@ be careful not to access device MMIO regions unless it is also prepared to handle a #VE. #VE on Private Pages --------------------- +~~~~~~~~~~~~~~~~~~~~ An access to private mappings can also cause a #VE. Since all kernel memory is also private memory, the kernel might theoretically need to @@ -145,7 +309,7 @@ The hypervisor is permitted to unilaterally move accepted pages to a to handle the exception. Linux #VE handler -================= +----------------- Just like page faults or #GP's, #VE exceptions can be either handled or be fatal. Typically, an unhandled userspace #VE results in a SIGSEGV. @@ -167,7 +331,7 @@ While the block is in place, any #VE is elevated to a double fault (#DF) which is not recoverable. MMIO handling -============= +------------- In non-TDX VMs, MMIO is usually implemented by giving a guest access to a mapping which will cause a VMEXIT on access, and then the hypervisor @@ -189,7 +353,7 @@ MMIO access via other means (like structure overlays) may result in an oops. Shared Memory Conversions -========================= +------------------------- All TDX guest memory starts out as private at boot. This memory can not be accessed by the hypervisor. However, some kernel users like device