From patchwork Thu Feb 16 06:18:12 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: ben@skyportsystems.com X-Patchwork-Id: 9576557 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 619CE6049F for ; Thu, 16 Feb 2017 06:26:01 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 50C6E28503 for ; Thu, 16 Feb 2017 06:26:01 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 41BC728535; Thu, 16 Feb 2017 06:26:01 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_HI,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 54FF628503 for ; Thu, 16 Feb 2017 06:26:00 +0000 (UTC) Received: from localhost ([::1]:44832 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ceFVv-0007aL-CD for patchwork-qemu-devel@patchwork.kernel.org; Thu, 16 Feb 2017 01:25:59 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48836) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ceFOm-00012q-KV for qemu-devel@nongnu.org; Thu, 16 Feb 2017 01:18:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ceFOk-0000RA-UR for qemu-devel@nongnu.org; Thu, 16 Feb 2017 01:18:36 -0500 Received: from mail-ot0-x22f.google.com ([2607:f8b0:4003:c0f::22f]:33541) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1ceFOk-0000QW-OI for qemu-devel@nongnu.org; Thu, 16 Feb 2017 01:18:34 -0500 Received: by mail-ot0-x22f.google.com with SMTP id 73so5303982otj.0 for ; Wed, 15 Feb 2017 22:18:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=skyportsystems.com; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :in-reply-to:references; bh=gSIFLHzPVQDCEeCLHubrulpnBKgxW6aeRBS2fyYxEzk=; b=Wxf7tky/7Xb6zHo789pAbOG+8RQP0yt2qwbtMu3j9DnvJanGZDuQ5QKEtqX0dW1kvA FURzNlJdL/XnabuSPpTZyuzo6c+wo0HWKWqhXi9/hoEG/dsDBN3fWCEXMnDxpnrkzul9 cBDCxDReAx06mH/bNgejWVa6W3xqHVJm2llqY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:in-reply-to:references; bh=gSIFLHzPVQDCEeCLHubrulpnBKgxW6aeRBS2fyYxEzk=; b=nm1QYKf1xr0grwJHuW8DNHvmWH+Q1DgILLOtxofoT07oxIr7tAo23Sl+Nqey2jjsMA DwxG3Vq+/2KN0ppJRBGDl/+X0Y0wjdUL2nZ4L3jMH1uot1KCxx2gfy8wSX+ZwwecuC9k Xn0osINqXI4me7F7wVfXRtB9f1dYn7odVcP4rNAY5Df7/jnrNonWf85Mii5W6N37KvxM aHpd5ls3eQIW5eMgiisY4NHwUi/2ldsLb3fhwyyPONhvGwbZ2LHGUNk+U8oKjEt2vkj+ d3tPgm5MHEKBM/cW0EWG6Op9FkAWEcvi1S8ulJVnvcCHU2L8cfLONSyE9oUL4n+cX3pM gwMQ== X-Gm-Message-State: AMke39nZKOSzFg7ba0vdqCyBoUtlXiW9KgsFPNQQeR1YIhpsMuTFBePrefm1IyOfaKy6cKOx X-Received: by 10.157.48.51 with SMTP id d48mr290621otc.207.1487225912865; Wed, 15 Feb 2017 22:18:32 -0800 (PST) Received: from Arrow.corp.skyportsystems.com (76-236-31-201.lightspeed.sntcca.sbcglobal.net. [76.236.31.201]) by smtp.gmail.com with ESMTPSA id c7sm2556036otb.55.2017.02.15.22.18.31 (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 15 Feb 2017 22:18:32 -0800 (PST) From: ben@skyportsystems.com To: qemu-devel@nongnu.org Date: Wed, 15 Feb 2017 22:18:12 -0800 Message-Id: <6e7af53f114f4875fbb952fb047d9d91bba2634f.1487224954.git.ben@skyportsystems.com> X-Mailer: git-send-email 2.10.1 (Apple Git-78) In-Reply-To: References: In-Reply-To: References: X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2607:f8b0:4003:c0f::22f Subject: [Qemu-devel] [PATCH v7 2/8] docs: VM Generation ID device description X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Gal Hammer , imammedo@redhat.com, lersek@redhat.com, Ben Warren , mst@redhat.com Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Ben Warren This patch is based off an earlier version by Gal Hammer (ghammer@redhat.com) Requirements section, ASCII diagrams and overall help provided by Laszlo Ersek (lersek@redhat.com) Signed-off-by: Gal Hammer Signed-off-by: Ben Warren Reviewed-by: Laszlo Ersek Reviewed-by: Igor Mammedov --- docs/specs/vmgenid.txt | 245 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 245 insertions(+) create mode 100644 docs/specs/vmgenid.txt diff --git a/docs/specs/vmgenid.txt b/docs/specs/vmgenid.txt new file mode 100644 index 0000000..aa9f518 --- /dev/null +++ b/docs/specs/vmgenid.txt @@ -0,0 +1,245 @@ +VIRTUAL MACHINE GENERATION ID +============================= + +Copyright (C) 2016 Red Hat, Inc. +Copyright (C) 2017 Skyport Systems, Inc. + +This work is licensed under the terms of the GNU GPL, version 2 or later. +See the COPYING file in the top-level directory. + +=== + +The VM generation ID (vmgenid) device is an emulated device which +exposes a 128-bit, cryptographically random, integer value identifier, +referred to as a Globally Unique Identifier, or GUID. + +This allows management applications (e.g. libvirt) to notify the guest +operating system when the virtual machine is executed with a different +configuration (e.g. snapshot execution or creation from a template). The +guest operating system notices the change, and is then able to react as +appropriate by marking its copies of distributed databases as dirty, +re-initializing its random number generator etc. + + +Requirements +------------ + +These requirements are extracted from the "How to implement virtual machine +generation ID support in a virtualization platform" section of the +specification, dated August 1, 2012. + + +The document may be found on the web at: + http://go.microsoft.com/fwlink/?LinkId=260709 + +R1a. The generation ID shall live in an 8-byte aligned buffer. + +R1b. The buffer holding the generation ID shall be in guest RAM, ROM, or device + MMIO range. + +R1c. The buffer holding the generation ID shall be kept separate from areas + used by the operating system. + +R1d. The buffer shall not be covered by an AddressRangeMemory or + AddressRangeACPI entry in the E820 or UEFI memory map. + +R1e. The generation ID shall not live in a page frame that could be mapped with + caching disabled. (In other words, regardless of whether the generation ID + lives in RAM, ROM or MMIO, it shall only be mapped as cacheable.) + +R2 to R5. [These AML requirements are isolated well enough in the Microsoft + specification for us to simply refer to them here.] + +R6. The hypervisor shall expose a _HID (hardware identifier) object in the + VMGenId device's scope that is unique to the hypervisor vendor. + + +QEMU Implementation +------------------- + +The above-mentioned specification does not dictate which ACPI descriptor table +will contain the VM Generation ID device. Other implementations (Hyper-V and +Xen) put it in the main descriptor table (Differentiated System Description +Table or DSDT). For ease of debugging and implementation, we have decided to +put it in its own Secondary System Description Table, or SSDT. + +The following is a dump of the contents from a running system: + +# iasl -p ./SSDT -d /sys/firmware/acpi/tables/SSDT + +Intel ACPI Component Architecture +ASL+ Optimizing Compiler version 20150717-64 +Copyright (c) 2000 - 2015 Intel Corporation + +Reading ACPI table from file /sys/firmware/acpi/tables/SSDT - Length +00000198 (0x0000C6) +ACPI: SSDT 0x0000000000000000 0000C6 (v01 BOCHS VMGENID 00000001 BXPC +00000001) +Acpi table [SSDT] successfully installed and loaded +Pass 1 parse of [SSDT] +Pass 2 parse of [SSDT] +Parsing Deferred Opcodes (Methods/Buffers/Packages/Regions) + +Parsing completed +Disassembly completed +ASL Output: ./SSDT.dsl - 1631 bytes +# cat SSDT.dsl +/* + * Intel ACPI Component Architecture + * AML/ASL+ Disassembler version 20150717-64 + * Copyright (c) 2000 - 2015 Intel Corporation + * + * Disassembling to symbolic ASL+ operators + * + * Disassembly of /sys/firmware/acpi/tables/SSDT, Sun Feb 5 00:19:37 2017 + * + * Original Table Header: + * Signature "SSDT" + * Length 0x000000CA (202) + * Revision 0x01 + * Checksum 0x4B + * OEM ID "BOCHS " + * OEM Table ID "VMGENID" + * OEM Revision 0x00000001 (1) + * Compiler ID "BXPC" + * Compiler Version 0x00000001 (1) + */ +DefinitionBlock ("/sys/firmware/acpi/tables/SSDT.aml", "SSDT", 1, "BOCHS ", +"VMGENID", 0x00000001) +{ + Name (VGIA, 0x07FFF000) + Scope (\_SB) + { + Device (VGEN) + { + Name (_HID, "QEMUVGID") // _HID: Hardware ID + Name (_CID, "VM_Gen_Counter") // _CID: Compatible ID + Name (_DDN, "VM_Gen_Counter") // _DDN: DOS Device Name + Method (_STA, 0, NotSerialized) // _STA: Status + { + Local0 = 0x0F + If ((VGIA == Zero)) + { + Local0 = Zero + } + + Return (Local0) + } + + Method (ADDR, 0, NotSerialized) + { + Local0 = Package (0x02) {} + Index (Local0, Zero) = (VGIA + 0x28) + Index (Local0, One) = Zero + Return (Local0) + } + } + } + + Method (\_GPE._E05, 0, NotSerialized) // _Exx: Edge-Triggered GPE + { + Notify (\_SB.VGEN, 0x80) // Status Change + } +} + + +Design Details: +--------------- + +Requirements R1a through R1e dictate that the memory holding the +VM Generation ID must be allocated and owned by the guest firmware, +in this case BIOS or UEFI. However, to be useful, QEMU must be able to +change the contents of the memory at runtime, specifically when starting a +backed-up or snapshotted image. In order to do this, QEMU must know the +address that has been allocated. + +The mechanism chosen for this memory sharing is writeable fw_cfg blobs. +These are data object that are visible to both QEMU and guests, and are +addressable as sequential files. + +More information about fw_cfg can be found in "docs/specs/fw_cfg.txt" + +Two fw_cfg blobs are used in this case: + +/etc/vmgenid_guid - contains the actual VM Generation ID GUID + - read-only to the guest +/etc/vmgenid_addr - contains the address of the downloaded vmgenid blob + - writeable by the guest + + +QEMU sends the following commands to the guest at startup: + +1. Allocate memory for vmgenid_guid fw_cfg blob. +2. Write the address of vmgenid_guid into the SSDT (VGIA ACPI variable as + shown above in the iasl dump). Note that this change is not propagated + back to QEMU. +3. Write the address of vmgenid_guid back to QEMU's copy of vmgenid_addr + via the fw_cfg DMA interface. + +After step 3, QEMU is able to update the contents of vmgenid_guid at will. + +Since BIOS or UEFI does not necessarily run when we wish to change the GUID, +the value of VGIA is persisted via the VMState mechanism. + +As spelled out in the specification, any change to the GUID executes an +ACPI notification. The exact handler to use is not specified, so the vmgenid +device uses the first unused one: \_GPE._E05. + + +Endian-ness Considerations: +--------------------------- + +Although not specified in Microsoft's document, it is assumed that the +device is expected to use little-endian format. + +All GUID passed in via command line or monitor are treated as big-endian. +GUID values displayed via monitor are shown in big-endian format. + + +GUID Storage Format: +-------------------- + +In order to implement an OVMF "SDT Header Probe Suppressor", the contents of +the vmgenid_guid fw_cfg blob are not simply a 128-bit GUID. There is also +significant padding in order to align and fill a memory page, as shown in the +following diagram: + ++----------------------------------+ +| SSDT with OEM Table ID = VMGENID | ++----------------------------------+ +| ... | TOP OF PAGE +| VGIA dword object ---------------|-----> +---------------------------+ +| ... | | fw-allocated array for | +| _STA method referring to VGIA | | "etc/vmgenid_guid" | +| ... | +---------------------------+ +| ADDR method referring to VGIA | | 0: OVMF SDT Header probe | +| ... | | suppressor | ++----------------------------------+ | 36: padding for 8-byte | + | alignment | + | 40: GUID | + | 56: padding to page size | + +---------------------------+ + END OF PAGE + + +Device Usage: +------------- + +The device has one property, which may be only be set using the command line: + + guid - sets the value of the GUID. A special value "auto" instructs + QEMU to generate a new random GUID. + +For example: + + QEMU -device vmgenid,guid="324e6eaf-d1d1-4bf6-bf41-b9bb6c91fb87" + QEMU -device vmgenid,guid=auto + +The property may be queried via QMP/HMP: + + (QEMU) query-vm-generation-id + {"return": {"guid": "324e6eaf-d1d1-4bf6-bf41-b9bb6c91fb87"}} + +Setting of this parameter is intentionally left out from the QMP/HMP +interfaces. There are no known use cases for changing the GUID once QEMU is +running, and adding this capability would greatly increase the complexity.