cachepc-qemu

Fork of AMDESE/qemu with changes for cachepc side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-qemu
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cpu-hotplug.rst (4133B)

      1===================
      2Virtual CPU hotplug
      3===================
      4
      5A complete example of vCPU hotplug (and hot-unplug) using QMP
      6``device_add`` and ``device_del``.
      7
      8vCPU hotplug
      9------------
     10
     11(1) Launch QEMU as follows (note that the "maxcpus" is mandatory to
     12    allow vCPU hotplug)::
     13
     14      $ qemu-system-x86_64 -display none -no-user-config -m 2048 \
     15          -nodefaults -monitor stdio -machine pc,accel=kvm,usb=off \
     16          -smp 1,maxcpus=2 -cpu IvyBridge-IBRS \
     17          -qmp unix:/tmp/qmp-sock,server=on,wait=off
     18
     19(2) Run 'qmp-shell' (located in the source tree, under: "scripts/qmp/)
     20    to connect to the just-launched QEMU::
     21
     22      $> ./qmp-shell -p -v /tmp/qmp-sock
     23      [...]
     24      (QEMU)
     25
     26(3) Find out which CPU types could be plugged, and into which sockets::
     27
     28      (QEMU) query-hotpluggable-cpus
     29      {
     30          "execute": "query-hotpluggable-cpus",
     31          "arguments": {}
     32      }
     33      {
     34          "return": [
     35              {
     36                  "type": "IvyBridge-IBRS-x86_64-cpu",
     37                  "vcpus-count": 1,
     38                  "props": {
     39                      "socket-id": 1,
     40                      "core-id": 0,
     41                      "thread-id": 0
     42                  }
     43              },
     44              {
     45                  "qom-path": "/machine/unattached/device[0]",
     46                  "type": "IvyBridge-IBRS-x86_64-cpu",
     47                  "vcpus-count": 1,
     48                  "props": {
     49                      "socket-id": 0,
     50                      "core-id": 0,
     51                      "thread-id": 0
     52                  }
     53              }
     54          ]
     55      }
     56      (QEMU)
     57
     58(4) The ``query-hotpluggable-cpus`` command returns an object for CPUs
     59    that are present (containing a "qom-path" member) or which may be
     60    hot-plugged (no "qom-path" member).  From its output in step (3), we
     61    can see that ``IvyBridge-IBRS-x86_64-cpu`` is present in socket 0,
     62    while hot-plugging a CPU into socket 1 requires passing the listed
     63    properties to QMP ``device_add``::
     64
     65      (QEMU) device_add id=cpu-2 driver=IvyBridge-IBRS-x86_64-cpu socket-id=1 core-id=0 thread-id=0
     66      {
     67          "execute": "device_add",
     68          "arguments": {
     69              "socket-id": 1,
     70              "driver": "IvyBridge-IBRS-x86_64-cpu",
     71              "id": "cpu-2",
     72              "core-id": 0,
     73              "thread-id": 0
     74          }
     75      }
     76      {
     77          "return": {}
     78      }
     79      (QEMU)
     80
     81(5) Optionally, run QMP ``query-cpus-fast`` for some details about the
     82    vCPUs::
     83
     84      (QEMU) query-cpus-fast
     85      {
     86          "execute": "query-cpus-fast",
     87          "arguments": {}
     88      }
     89      {
     90          "return": [
     91              {
     92                  "qom-path": "/machine/unattached/device[0]",
     93                  "target": "x86_64",
     94                  "thread-id": 11534,
     95                  "cpu-index": 0,
     96                  "props": {
     97                      "socket-id": 0,
     98                      "core-id": 0,
     99                      "thread-id": 0
    100                  },
    101                  "arch": "x86"
    102              },
    103              {
    104                  "qom-path": "/machine/peripheral/cpu-2",
    105                  "target": "x86_64",
    106                  "thread-id": 12106,
    107                  "cpu-index": 1,
    108                  "props": {
    109                      "socket-id": 1,
    110                      "core-id": 0,
    111                      "thread-id": 0
    112                  },
    113                  "arch": "x86"
    114              }
    115          ]
    116      }
    117      (QEMU)
    118
    119vCPU hot-unplug
    120---------------
    121
    122From the 'qmp-shell', invoke the QMP ``device_del`` command::
    123
    124      (QEMU) device_del id=cpu-2
    125      {
    126          "execute": "device_del",
    127          "arguments": {
    128              "id": "cpu-2"
    129          }
    130      }
    131      {
    132          "return": {}
    133      }
    134      (QEMU)
    135
    136.. note::
    137    vCPU hot-unplug requires guest cooperation; so the ``device_del``
    138    command above does not guarantee vCPU removal -- it's a "request to
    139    unplug".  At this point, the guest will get a System Control
    140    Interrupt (SCI) and calls the ACPI handler for the affected vCPU
    141    device.  Then the guest kernel will bring the vCPU offline and tell
    142    QEMU to unplug it.