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