docs/specs/vmgenid: Convert to rST
Convert docs/specs/vmgenid.txt to rST format. Reviewed-by: Ani Sinha <anisinha@redhat.com> Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Message-id: 20230927151205.70930-9-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell
parent
096d3ce231
commit
912fb3678b
@ -2437,7 +2437,7 @@ S: Orphan
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R: Ani Sinha <ani@anisinha.ca>
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F: hw/acpi/vmgenid.c
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F: include/hw/acpi/vmgenid.h
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F: docs/specs/vmgenid.txt
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F: docs/specs/vmgenid.rst
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F: tests/qtest/vmgenid-test.c
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LED
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@ -31,3 +31,4 @@ guest hardware that is specific to QEMU.
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standard-vga
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virt-ctlr
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vmcoreinfo
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vmgenid
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246
docs/specs/vmgenid.rst
Normal file
246
docs/specs/vmgenid.rst
Normal file
@ -0,0 +1,246 @@
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Virtual Machine Generation ID Device
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====================================
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..
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Copyright (C) 2016 Red Hat, Inc.
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Copyright (C) 2017 Skyport Systems, Inc.
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This work is licensed under the terms of the GNU GPL, version 2 or later.
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See the COPYING file in the top-level directory.
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The VM generation ID (``vmgenid``) device is an emulated device which
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exposes a 128-bit, cryptographically random, integer value identifier,
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referred to as a Globally Unique Identifier, or GUID.
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This allows management applications (e.g. libvirt) to notify the guest
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operating system when the virtual machine is executed with a different
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configuration (e.g. snapshot execution or creation from a template). The
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guest operating system notices the change, and is then able to react as
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appropriate by marking its copies of distributed databases as dirty,
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re-initializing its random number generator etc.
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Requirements
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------------
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These requirements are extracted from the "How to implement virtual machine
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generation ID support in a virtualization platform" section of
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`the Microsoft Virtual Machine Generation ID specification
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<http://go.microsoft.com/fwlink/?LinkId=260709>`_ dated August 1, 2012.
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- **R1a** The generation ID shall live in an 8-byte aligned buffer.
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- **R1b** The buffer holding the generation ID shall be in guest RAM,
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ROM, or device MMIO range.
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- **R1c** The buffer holding the generation ID shall be kept separate from
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areas used by the operating system.
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- **R1d** The buffer shall not be covered by an AddressRangeMemory or
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AddressRangeACPI entry in the E820 or UEFI memory map.
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- **R1e** The generation ID shall not live in a page frame that could be
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mapped with caching disabled. (In other words, regardless of whether the
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generation ID lives in RAM, ROM or MMIO, it shall only be mapped as
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cacheable.)
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- **R2** to **R5** [These AML requirements are isolated well enough in the
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Microsoft specification for us to simply refer to them here.]
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- **R6** The hypervisor shall expose a _HID (hardware identifier) object
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in the VMGenId device's scope that is unique to the hypervisor vendor.
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QEMU Implementation
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-------------------
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The above-mentioned specification does not dictate which ACPI descriptor table
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will contain the VM Generation ID device. Other implementations (Hyper-V and
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Xen) put it in the main descriptor table (Differentiated System Description
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Table or DSDT). For ease of debugging and implementation, we have decided to
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put it in its own Secondary System Description Table, or SSDT.
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The following is a dump of the contents from a running system::
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# iasl -p ./SSDT -d /sys/firmware/acpi/tables/SSDT
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Intel ACPI Component Architecture
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ASL+ Optimizing Compiler version 20150717-64
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Copyright (c) 2000 - 2015 Intel Corporation
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Reading ACPI table from file /sys/firmware/acpi/tables/SSDT - Length
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00000198 (0x0000C6)
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ACPI: SSDT 0x0000000000000000 0000C6 (v01 BOCHS VMGENID 00000001 BXPC 00000001)
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Acpi table [SSDT] successfully installed and loaded
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Pass 1 parse of [SSDT]
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Pass 2 parse of [SSDT]
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Parsing Deferred Opcodes (Methods/Buffers/Packages/Regions)
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Parsing completed
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Disassembly completed
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ASL Output: ./SSDT.dsl - 1631 bytes
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# cat SSDT.dsl
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/*
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* Intel ACPI Component Architecture
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* AML/ASL+ Disassembler version 20150717-64
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* Copyright (c) 2000 - 2015 Intel Corporation
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*
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* Disassembling to symbolic ASL+ operators
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*
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* Disassembly of /sys/firmware/acpi/tables/SSDT, Sun Feb 5 00:19:37 2017
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*
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* Original Table Header:
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* Signature "SSDT"
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* Length 0x000000CA (202)
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* Revision 0x01
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* Checksum 0x4B
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* OEM ID "BOCHS "
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* OEM Table ID "VMGENID"
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* OEM Revision 0x00000001 (1)
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* Compiler ID "BXPC"
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* Compiler Version 0x00000001 (1)
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*/
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DefinitionBlock ("/sys/firmware/acpi/tables/SSDT.aml", "SSDT", 1, "BOCHS ", "VMGENID", 0x00000001)
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{
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Name (VGIA, 0x07FFF000)
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Scope (\_SB)
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{
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Device (VGEN)
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{
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Name (_HID, "QEMUVGID") // _HID: Hardware ID
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Name (_CID, "VM_Gen_Counter") // _CID: Compatible ID
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Name (_DDN, "VM_Gen_Counter") // _DDN: DOS Device Name
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Method (_STA, 0, NotSerialized) // _STA: Status
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{
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Local0 = 0x0F
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If ((VGIA == Zero))
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{
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Local0 = Zero
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}
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Return (Local0)
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}
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Method (ADDR, 0, NotSerialized)
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{
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Local0 = Package (0x02) {}
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Index (Local0, Zero) = (VGIA + 0x28)
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Index (Local0, One) = Zero
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Return (Local0)
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}
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}
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}
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Method (\_GPE._E05, 0, NotSerialized) // _Exx: Edge-Triggered GPE
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{
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Notify (\_SB.VGEN, 0x80) // Status Change
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}
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}
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Design Details:
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---------------
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Requirements R1a through R1e dictate that the memory holding the
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VM Generation ID must be allocated and owned by the guest firmware,
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in this case BIOS or UEFI. However, to be useful, QEMU must be able to
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change the contents of the memory at runtime, specifically when starting a
|
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backed-up or snapshotted image. In order to do this, QEMU must know the
|
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address that has been allocated.
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The mechanism chosen for this memory sharing is writable fw_cfg blobs.
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These are data object that are visible to both QEMU and guests, and are
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addressable as sequential files.
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More information about fw_cfg can be found in :doc:`fw_cfg`.
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Two fw_cfg blobs are used in this case:
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``/etc/vmgenid_guid``
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- contains the actual VM Generation ID GUID
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- read-only to the guest
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``/etc/vmgenid_addr``
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- contains the address of the downloaded vmgenid blob
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- writable by the guest
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QEMU sends the following commands to the guest at startup:
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1. Allocate memory for vmgenid_guid fw_cfg blob.
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2. Write the address of vmgenid_guid into the SSDT (VGIA ACPI variable as
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shown above in the iasl dump). Note that this change is not propagated
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back to QEMU.
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3. Write the address of vmgenid_guid back to QEMU's copy of vmgenid_addr
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via the fw_cfg DMA interface.
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After step 3, QEMU is able to update the contents of vmgenid_guid at will.
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Since BIOS or UEFI does not necessarily run when we wish to change the GUID,
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the value of VGIA is persisted via the VMState mechanism.
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As spelled out in the specification, any change to the GUID executes an
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ACPI notification. The exact handler to use is not specified, so the vmgenid
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device uses the first unused one: ``\_GPE._E05``.
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Endian-ness Considerations:
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---------------------------
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Although not specified in Microsoft's document, it is assumed that the
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device is expected to use little-endian format.
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All GUID passed in via command line or monitor are treated as big-endian.
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GUID values displayed via monitor are shown in big-endian format.
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GUID Storage Format:
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--------------------
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In order to implement an OVMF "SDT Header Probe Suppressor", the contents of
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the vmgenid_guid fw_cfg blob are not simply a 128-bit GUID. There is also
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significant padding in order to align and fill a memory page, as shown in the
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following diagram::
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+----------------------------------+
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| SSDT with OEM Table ID = VMGENID |
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+----------------------------------+
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| ... | TOP OF PAGE
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| VGIA dword object ---------------|-----> +---------------------------+
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| ... | | fw-allocated array for |
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| _STA method referring to VGIA | | "etc/vmgenid_guid" |
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| ... | +---------------------------+
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| ADDR method referring to VGIA | | 0: OVMF SDT Header probe |
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| ... | | suppressor |
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+----------------------------------+ | 36: padding for 8-byte |
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| alignment |
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| 40: GUID |
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| 56: padding to page size |
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+---------------------------+
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END OF PAGE
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Device Usage:
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-------------
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The device has one property, which may be only be set using the command line:
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``guid``
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sets the value of the GUID. A special value ``auto`` instructs
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QEMU to generate a new random GUID.
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For example::
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QEMU -device vmgenid,guid="324e6eaf-d1d1-4bf6-bf41-b9bb6c91fb87"
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QEMU -device vmgenid,guid=auto
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The property may be queried via QMP/HMP::
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(QEMU) query-vm-generation-id
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{"return": {"guid": "324e6eaf-d1d1-4bf6-bf41-b9bb6c91fb87"}}
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Setting of this parameter is intentionally left out from the QMP/HMP
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interfaces. There are no known use cases for changing the GUID once QEMU is
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running, and adding this capability would greatly increase the complexity.
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@ -1,245 +0,0 @@
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VIRTUAL MACHINE GENERATION ID
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=============================
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Copyright (C) 2016 Red Hat, Inc.
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Copyright (C) 2017 Skyport Systems, Inc.
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This work is licensed under the terms of the GNU GPL, version 2 or later.
|
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See the COPYING file in the top-level directory.
|
||||
|
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===
|
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|
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The VM generation ID (vmgenid) device is an emulated device which
|
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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.
|
||||
|
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|
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The document may be found on the web at:
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http://go.microsoft.com/fwlink/?LinkId=260709
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|
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R1a. The generation ID shall live in an 8-byte aligned buffer.
|
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|
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R1b. The buffer holding the generation ID shall be in guest RAM, ROM, or device
|
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MMIO range.
|
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|
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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
|
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00000001)
|
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Acpi table [SSDT] successfully installed and loaded
|
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Pass 1 parse of [SSDT]
|
||||
Pass 2 parse of [SSDT]
|
||||
Parsing Deferred Opcodes (Methods/Buffers/Packages/Regions)
|
||||
|
||||
Parsing completed
|
||||
Disassembly completed
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ASL Output: ./SSDT.dsl - 1631 bytes
|
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# cat SSDT.dsl
|
||||
/*
|
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* Intel ACPI Component Architecture
|
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* 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 "
|
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* OEM Table ID "VMGENID"
|
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* OEM Revision 0x00000001 (1)
|
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* Compiler ID "BXPC"
|
||||
* Compiler Version 0x00000001 (1)
|
||||
*/
|
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DefinitionBlock ("/sys/firmware/acpi/tables/SSDT.aml", "SSDT", 1, "BOCHS ",
|
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"VMGENID", 0x00000001)
|
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{
|
||||
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 writable 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
|
||||
- writable 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.
|
||||
Loading…
Reference in New Issue
Block a user