On 02/15/17 12:07, Igor Mammedov wrote: > On Tue, 14 Feb 2017 22:15:44 -0800 > b...@skyportsystems.com wrote: > >> From: Ben Warren <b...@skyportsystems.com> >> >> This patch is based off an earlier version by >> Gal Hammer (gham...@redhat.com) >> >> Requirements section, ASCII diagrams and overall help >> provided by Laszlo Ersek (ler...@redhat.com) >> >> Signed-off-by: Gal Hammer <gham...@redhat.com> >> Signed-off-by: Ben Warren <b...@skyportsystems.com> >> Reviewed-by: Laszlo Ersek <ler...@redhat.com> > Reviewed-by: Igor Mammedov <imamm...@redhat.com>
I meticulously compared this version against the docs patch in v5, and I agree that it's a good update. I also see that [PATCH v6 4/7] ACPI: Add Virtual Machine Generation ID support adds a reference to this file, as a comment, which was requested by Igor. Looks good! My R-b stands. Thank you, Laszlo >> --- >> 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. >