docs/specs/acpi_mem_hotplug.txt

   1 QEMU<->ACPI BIOS memory hotplug interface
   2 --------------------------------------
   3
   4 ACPI BIOS GPE.3 handler is dedicated for notifying OS about memory hot-add
   5 and hot-remove events.
   6
   7 Memory hot-plug interface (IO port 0xa00-0xa17, 1-4 byte access):
   8 ---------------------------------------------------------------
   9 0xa00:
  10   read access:
  11       [0x0-0x3] Lo part of memory device phys address
  12       [0x4-0x7] Hi part of memory device phys address
  13       [0x8-0xb] Lo part of memory device size in bytes
  14       [0xc-0xf] Hi part of memory device size in bytes
  15       [0x10-0x13] Memory device proximity domain
  16       [0x14] Memory device status fields
  17           bits:
  18               0: Device is enabled and may be used by guest
  19               1: Device insert event, used to distinguish device for which
  20                  no device check event to OSPM was issued.
  21                  It's valid only when bit 1 is set.
  22               2: Device remove event, used to distinguish device for which
  23                  no device eject request to OSPM was issued.
  24               3-7: reserved and should be ignored by OSPM
  25       [0x15-0x17] reserved
  26
  27   write access:
  28       [0x0-0x3] Memory device slot selector, selects active memory device.
  29                 All following accesses to other registers in 0xa00-0xa17
  30                 region will read/store data from/to selected memory device.
  31       [0x4-0x7] OST event code reported by OSPM
  32       [0x8-0xb] OST status code reported by OSPM
  33       [0xc-0x13] reserved, writes into it are ignored
  34       [0x14] Memory device control fields
  35           bits:
  36               0: reserved, OSPM must clear it before writing to register.
  37                  Due to BUG in versions prior 2.4 that field isn't cleared
  38                  when other fields are written. Keep it reserved and don't
  39                  try to reuse it.
  40               1: if set to 1 clears device insert event, set by OSPM
  41                  after it has emitted device check event for the
  42                  selected memory device
  43               2: if set to 1 clears device remove event, set by OSPM
  44                  after it has emitted device eject request for the
  45                  selected memory device
  46               3: if set to 1 initiates device eject, set by OSPM when it
  47                  triggers memory device removal and calls _EJ0 method
  48               4-7: reserved, OSPM must clear them before writing to register
  49
  50 Selecting memory device slot beyond present range has no effect on platform:
  51    - write accesses to memory hot-plug registers not documented above are
  52      ignored
  53    - read accesses to memory hot-plug registers not documented above return
  54      all bits set to 1.
  55
  56 Memory hot remove process diagram:
  57 ----------------------------------
  58  +-------------+     +-----------------------+      +------------------+
  59  |  1. QEMU    |     | 2. QEMU               |      |3. QEMU           |
  60  |  device_del +---->+ device unplug request +----->+Send SCI to guest,|
  61  |             |     |         cb            |      |return control to |
  62  +-------------+     +-----------------------+      |management        |
  63                                                     +------------------+
  64
  65  +---------------------------------------------------------------------+
  66
  67  +---------------------+              +-------------------------+
  68  | OSPM:               | remove event | OSPM:                   |
  69  | send Eject Request, |              | Scan memory devices     |
  70  | clear remove event  +<-------------+ for event flags         |
  71  |                     |              |                         |
  72  +---------------------+              +-------------------------+
  73            |
  74            |
  75  +---------v--------+            +-----------------------+
  76  | Guest OS:        |  success   | OSPM:                 |
  77  | process Ejection +----------->+ Execute _EJ0 method,  |
  78  | request          |            | set eject bit in flags|
  79  +------------------+            +-----------------------+
  80            |failure                         |
  81            v                                v
  82  +------------------------+      +-----------------------+
  83  | OSPM:                  |      | QEMU:                 |
  84  | set OST event & status |      | call device unplug cb |
  85  | fields                 |      |                       |
  86  +------------------------+      +-----------------------+
  87           |                                  |
  88           v                                  v
  89  +------------------+              +-------------------+
  90  |QEMU:             |              |QEMU:              |
  91  |Send OST QMP event|              |Send device deleted|
  92  |                  |              |QMP event          |
  93  +------------------+              |                   |
  94                                    +-------------------+