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

MAINTAINERS

@@ -2437,7 +2437,7 @@ S: Orphan
 R: Ani Sinha <ani@anisinha.ca>
 F: hw/acpi/vmgenid.c
 F: include/hw/acpi/vmgenid.h
-F: docs/specs/vmgenid.txt
+F: docs/specs/vmgenid.rst
 F: tests/qtest/vmgenid-test.c
 
 LED

docs/specs/index.rst

@@ -31,3 +31,4 @@ guest hardware that is specific to QEMU.
    standard-vga
    virt-ctlr
    vmcoreinfo
+   vmgenid

docs/specs/vmgenid.rst

@@ -0,0 +1,246 @@
+Virtual Machine Generation ID Device
+====================================
+
+..
+   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 Microsoft Virtual Machine Generation ID specification
+<http://go.microsoft.com/fwlink/?LinkId=260709>`_ dated August 1, 2012.
+
+- **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 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 :doc:`fw_cfg`.
+
+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.

docs/specs/vmgenid.txt

@@ -1,245 +0,0 @@
-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 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.