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= 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:
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, 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, and in our case amounts to using "C<n>"
for PCI/VIO device slots, where <n> is unique across all PCI/VIO
device slots.
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
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.
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.
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
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
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
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
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)
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.
The format for these EPOW-signalled events is described below under
"hotplug/unplug event structure". Note that these events are not
formally part of the PAPR+ specification, and have been superseded by a
newer format, also described below under "hotplug/unplug event structure",
and so are now deemed a "legacy" format. The formats are similar, but the
"modern" format contains additional fields/flags, which are denoted for the
purposes of this documentation with "#ifdef GUEST_SUPPORTS_MODERN" guards.
QEMU should assume support only for "legacy" fields/flags unless the guest
advertises support for the "modern" format via ibm,client-architecture-support
hcall by setting byte 5, bit 6 of it's ibm,architecture-vec-5 option vector
structure (as described by LoPAPR v11, B.6.2.3). As with "legacy" format events,
"modern" format events are surfaced to the guest via check-exception RTAS calls,
but use a dedicated event source to signal the guest. This event source is
advertised to the guest by the addition of a "hot-plug-events" node under
"/event-sources" node of the guest's device tree using the standard format
described in LoPAPR v11, B.6.12.1.
== hotplug/unplug event structure ==
The hotplug-specific payload in QEMU is 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;
uint8_t hotplug_type; /* type of resource/device */
uint8_t hotplug_action; /* action (add/remove) */
uint8_t hotplug_identifier; /* type of the resource identifier,
* which serves as the discriminator
* for the 'drc' union field below
uint8_t capabilities; /* capability flags, currently unused
* by QEMU
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)
struct {
uint32_t count; /* number of DR resources to take
* action on
uint32_t index; /* DRC index of first resource to take
* action on. guest will take action
* on DRC index <index> through
* DRC index <index + count - 1> in
* sequential order
} count_indexed;
char name[1]; /* string representing the name of the
* DRC to take action on
} drc;
== ibm,lrdr-capacity ==
ibm,lrdr-capacity is a property in the /rtas device tree node that identifies
the dynamic reconfiguration capabilities of the guest. It consists of a triple
consisting of <phys>, <size> and <maxcpus>.
<phys>, encoded in BE format represents the maximum address in bytes and
hence the maximum memory that can be allocated to the guest.
<size>, encoded in BE format represents the size increments in which
memory can be hot-plugged to the guest.
<maxcpus>, a BE-encoded integer, represents the maximum number of
processors that the guest can have.
pseries guests use this property to note the maximum allowed CPUs for the
== ibm,dynamic-reconfiguration-memory ==
ibm,dynamic-reconfiguration-memory is a device tree node that represents
dynamically reconfigurable logical memory blocks (LMB). This node
is generated only when the guest advertises the support for it via
ibm,client-architecture-support call. Memory that is not dynamically
reconfigurable is represented by /memory nodes. The properties of this
node that are of interest to the sPAPR memory hotplug implementation
in QEMU are described here.
This 64bit integer defines the size of each dynamically reconfigurable LMB.
This property defines a lookup array in which the NUMA associativity
information for each LMB can be found. It is a property encoded array
that begins with an integer M, the number of associativity lists followed
by an integer N, the number of entries per associativity list and terminated
by M associativity lists each of length N integers.
This property provides the same information as given by ibm,associativity
property in a /memory node. Each assigned LMB has an index value between
0 and M-1 which is used as an index into this table to select which
associativity list to use for the LMB. This index value for each LMB
is defined in ibm,dynamic-memory property.
This property describes the dynamically reconfigurable memory. It is a
property encoded array that has an integer N, the number of LMBs followed
by N LMB list entires.
Each LMB list entry consists of the following elements:
- Logical address of the start of the LMB encoded as a 64bit integer. This
corresponds to reg property in /memory node.
- DRC index of the LMB that corresponds to ibm,my-drc-index property
in a /memory node.
- Four bytes reserved for expansion.
- Associativity list index for the LMB that is used as an index into
ibm,associativity-lookup-arrays property described earlier. This
is used to retrieve the right associativity list to be used for this
- A 32bit flags word. The bit at bit position 0x00000008 defines whether
the LMB is assigned to the the partition as of boot time.