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diff --git a/docs/specs/ppc-spapr-hotplug.txt b/docs/specs/ppc-spapr-hotplug.txt new file mode 100644 index 0000000000..d35771cc2b --- /dev/null +++ b/docs/specs/ppc-spapr-hotplug.txt @@ -0,0 +1,287 @@ += sPAPR Dynamic Reconfiguration = + +sPAPR/"pseries" guests make use of a facility called dynamic-reconfiguration +to handle hotplugging of dynamic "physical" resources like PCI cards, or +"logical"/paravirtual resources like memory, CPUs, and "physical" +host-bridges, which are generally managed by the host/hypervisor and provided +to guests as virtualized resources. The specifics of dynamic-reconfiguration +are documented extensively in PAPR+ v2.7, Section 13.1. This document +provides a summary of that information as it applies to the implementation +within QEMU. + +== Dynamic-reconfiguration Connectors == + +To manage hotplug/unplug of these resources, a firmware abstraction known as +a Dynamic Resource Connector (DRC) is used to assign a particular dynamic +resource to the guest, and provide an interface for the guest to manage +configuration/removal of the resource associated with it. + +== Device-tree description of DRCs == + +A set of 4 Open Firmware device tree array properties are used to describe +the name/index/power-domain/type of each DRC allocated to a guest at +boot-time. There may be multiple sets of these arrays, rooted at different +paths in the device tree depending on the type of resource the DRCs manage. + +In some cases, the DRCs themselves may be provided by a dynamic resource, +such as the DRCs managing PCI slots on a hotplugged PHB. In this case the +arrays would be fetched as part of the device tree retrieval interfaces +for hotplugged resources described under "Guest->Host interface". + +The array properties are described below. Each entry/element in an array +describes the DRC identified by the element in the corresponding position +of ibm,drc-indexes: + +ibm,drc-names: + first 4-bytes: BE-encoded integer denoting the number of entries + each entry: a NULL-terminated <name> string encoded as a byte array + + <name> values for logical/virtual resources are defined in PAPR+ v2.7, + Section 13.5.2.4, and basically consist of the type of the resource + followed by a space and a numerical value that's unique across resources + of that type. + + <name> values for "physical" resources such as PCI or VIO devices are + defined as being "location codes", which are the "location labels" of + each encapsulating device, starting from the chassis down to the + individual slot for the device, concatenated by a hyphen. This provides + a mapping of resources to a physical location in a chassis for debugging + purposes. For QEMU, this mapping is less important, so we assign a + location code that conforms to naming specifications, but is simply a + location label for the slot by itself to simplify the implementation. + The naming convention for location labels is documented in detail in + PAPR+ v2.7, Section 12.3.1.5, and in our case amounts to using "C<n>" + for PCI/VIO device slots, where <n> is unique across all PCI/VIO + device slots. + +ibm,drc-indexes: + first 4-bytes: BE-encoded integer denoting the number of entries + each 4-byte entry: BE-encoded <index> integer that is unique across all DRCs + in the machine + + <index> is arbitrary, but in the case of QEMU we try to maintain the + convention used to assign them to pSeries guests on pHyp: + + bit[31:28]: integer encoding of <type>, where <type> is: + 1 for CPU resource + 2 for PHB resource + 3 for VIO resource + 4 for PCI resource + 8 for Memory resource + bit[27:0]: integer encoding of <id>, where <id> is unique across + all resources of specified type + +ibm,drc-power-domains: + first 4-bytes: BE-encoded integer denoting the number of entries + each 4-byte entry: 32-bit, BE-encoded <index> integer that specifies the + power domain the resource will be assigned to. In the case of QEMU + we associated all resources with a "live insertion" domain, where the + power is assumed to be managed automatically. The integer value for + this domain is a special value of -1. + + +ibm,drc-types: + first 4-bytes: BE-encoded integer denoting the number of entries + each entry: a NULL-terminated <type> string encoded as a byte array + + <type> is assigned as follows: + "CPU" for a CPU + "PHB" for a physical host-bridge + "SLOT" for a VIO slot + "28" for a PCI slot + "MEM" for memory resource + +== Guest->Host interface to manage dynamic resources == + +Each DRC is given a globally unique DRC Index, and resources associated with +a particular DRC are configured/managed by the guest via a number of RTAS +calls which reference individual DRCs based on the DRC index. This can be +considered the guest->host interface. + +rtas-set-power-level: + arg[0]: integer identifying power domain + arg[1]: new power level for the domain, 0-100 + output[0]: status, 0 on success + output[1]: power level after command + + Set the power level for a specified power domain + +rtas-get-power-level: + arg[0]: integer identifying power domain + output[0]: status, 0 on success + output[1]: current power level + + Get the power level for a specified power domain + +rtas-set-indicator: + arg[0]: integer identifying sensor/indicator type + arg[1]: index of sensor, for DR-related sensors this is generally the + DRC index + arg[2]: desired sensor value + output[0]: status, 0 on success + + Set the state of an indicator or sensor. For the purpose of this document we + focus on the indicator/sensor types associated with a DRC. The types are: + + 9001: isolation-state, controls/indicates whether a device has been made + accessible to a guest + + supported sensor values: + 0: isolate, device is made unaccessible by guest OS + 1: unisolate, device is made available to guest OS + + 9002: dr-indicator, controls "visual" indicator associated with device + + supported sensor values: + 0: inactive, resource may be safely removed + 1: active, resource is in use and cannot be safely removed + 2: identify, used to visually identify slot for interactive hotplug + 3: action, in most cases, used in the same manner as identify + + 9003: allocation-state, generally only used for "logical" DR resources to + request the allocation/deallocation of a resource prior to acquiring + it via isolation-state->unisolate, or after releasing it via + isolation-state->isolate, respectively. for "physical" DR (like PCI + hotplug/unplug) the pre-allocation of the resource is implied and + this sensor is unused. + + supported sensor values: + 0: unusable, tell firmware/system the resource can be + unallocated/reclaimed and added back to the system resource pool + 1: usable, request the resource be allocated/reserved for use by + guest OS + 2: exchange, used to allocate a spare resource to use for fail-over + in certain situations. unused in QEMU + 3: recover, used to reclaim a previously allocated resource that's + not currently allocated to the guest OS. unused in QEMU + +rtas-get-sensor-state: + arg[0]: integer identifying sensor/indicator type + arg[1]: index of sensor, for DR-related sensors this is generally the + DRC index + output[0]: status, 0 on success + + Used to read an indicator or sensor value. + + For DR-related operations, the only noteworthy sensor is dr-entity-sense, + which has a type value of 9003, as allocation-state does in the case of + rtas-set-indicator. The semantics/encodings of the sensor values are distinct + however: + + supported sensor values for dr-entity-sense (9003) sensor: + 0: empty, + for physical resources: DRC/slot is empty + for logical resources: unused + 1: present, + for physical resources: DRC/slot is populated with a device/resource + for logical resources: resource has been allocated to the DRC + 2: unusable, + for physical resources: unused + for logical resources: DRC has no resource allocated to it + 3: exchange, + for physical resources: unused + for logical resources: resource available for exchange (see + allocation-state sensor semantics above) + 4: recovery, + for physical resources: unused + for logical resources: resource available for recovery (see + allocation-state sensor semantics above) + +rtas-ibm-configure-connector: + arg[0]: guest physical address of 4096-byte work area buffer + arg[1]: 0, or address of additional 4096-byte work area buffer. only non-zero + if a prior RTAS response indicated a need for additional memory + output[0]: status: + 0: completed transmittal of device-tree node + 1: instruct guest to prepare for next DT sibling node + 2: instruct guest to prepare for next DT child node + 3: instruct guest to prepare for next DT property + 4: instruct guest to ascend to parent DT node + 5: instruct guest to provide additional work-area buffer + via arg[1] + 990x: instruct guest that operation took too long and to try + again later + + Used to fetch an OF device-tree description of the resource associated with + a particular DRC. The DRC index is encoded in the first 4-bytes of the first + work area buffer. + + Work area layout, using 4-byte offsets: + wa[0]: DRC index of the DRC to fetch device-tree nodes from + wa[1]: 0 (hard-coded) + wa[2]: for next-sibling/next-child response: + wa offset of null-terminated string denoting the new node's name + for next-property response: + wa offset of null-terminated string denoting new property's name + wa[3]: for next-property response (unused otherwise): + byte-length of new property's value + wa[4]: for next-property response (unused otherwise): + new property's value, encoded as an OFDT-compatible byte array + +== hotplug/unplug events == + +For most DR operations, the hypervisor will issue host->guest add/remove events +using the EPOW/check-exception notification framework, where the host issues a +check-exception interrupt, then provides an RTAS event log via an +rtas-check-exception call issued by the guest in response. This framework is +documented by PAPR+ v2.7, and already use in by QEMU for generating powerdown +requests via EPOW events. + +For DR, this framework has been extended to include hotplug events, which were +previously unneeded due to direct manipulation of DR-related guest userspace +tools by host-level management such as an HMC. This level of management is not +applicable to PowerKVM, hence the reason for extending the notification +framework to support hotplug events. + +Note that these events are not yet formally part of the PAPR+ specification, +but support for this format has already been implemented in DR-related +guest tools such as powerpc-utils/librtas, as well as kernel patches that have +been submitted to handle in-kernel processing of memory/cpu-related hotplug +events[1], and is planned for formal inclusion is PAPR+ specification. The +hotplug-specific payload is QEMU implemented as follows (with all values +encoded in big-endian format): + +struct rtas_event_log_v6_hp { +#define SECTION_ID_HOTPLUG 0x4850 /* HP */ + struct section_header { + uint16_t section_id; /* set to SECTION_ID_HOTPLUG */ + uint16_t section_length; /* sizeof(rtas_event_log_v6_hp), + * plus the length of the DRC name + * if a DRC name identifier is + * specified for hotplug_identifier + */ + uint8_t section_version; /* version 1 */ + uint8_t section_subtype; /* unused */ + uint16_t creator_component_id; /* unused */ + } hdr; +#define RTAS_LOG_V6_HP_TYPE_CPU 1 +#define RTAS_LOG_V6_HP_TYPE_MEMORY 2 +#define RTAS_LOG_V6_HP_TYPE_SLOT 3 +#define RTAS_LOG_V6_HP_TYPE_PHB 4 +#define RTAS_LOG_V6_HP_TYPE_PCI 5 + uint8_t hotplug_type; /* type of resource/device */ +#define RTAS_LOG_V6_HP_ACTION_ADD 1 +#define RTAS_LOG_V6_HP_ACTION_REMOVE 2 + uint8_t hotplug_action; /* action (add/remove) */ +#define RTAS_LOG_V6_HP_ID_DRC_NAME 1 +#define RTAS_LOG_V6_HP_ID_DRC_INDEX 2 +#define RTAS_LOG_V6_HP_ID_DRC_COUNT 3 + uint8_t hotplug_identifier; /* type of the resource identifier, + * which serves as the discriminator + * for the 'drc' union field below + */ + uint8_t reserved; + union { + uint32_t index; /* DRC index of resource to take action + * on + */ + uint32_t count; /* number of DR resources to take + * action on (guest chooses which) + */ + char name[1]; /* string representing the name of the + * DRC to take action on + */ + } drc; +} QEMU_PACKED; + +[1] http://thread.gmane.org/gmane.linux.ports.ppc.embedded/75350/focus=106867 |