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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css.rst (3200B)

      1The virtual channel subsystem
      2=============================
      3
      4QEMU implements a virtual channel subsystem with subchannels, (mostly
      5functionless) channel paths, and channel devices (virtio-ccw, 3270, and
      6devices passed via vfio-ccw). It supports multiple subchannel sets (MSS) and
      7multiple channel subsystems extended (MCSS-E).
      8
      9All channel devices support the ``devno`` property, which takes a parameter
     10in the form ``<cssid>.<ssid>.<device number>``.
     11
     12The default channel subsystem image id (``<cssid>``) is ``0xfe``. Devices in
     13there will show up in channel subsystem image ``0`` to guests that do not
     14enable MCSS-E. Note that devices with a different cssid will not be visible
     15if the guest OS does not enable MCSS-E (which is true for all supported guest
     16operating systems today).
     17
     18Supported values for the subchannel set id (``<ssid>``) range from ``0-3``.
     19Devices with a ssid that is not ``0`` will not be visible if the guest OS
     20does not enable MSS (any Linux version that supports virtio also enables MSS).
     21Any device may be put into any subchannel set, there is no restriction by
     22device type.
     23
     24The device number can range from ``0-0xffff``.
     25
     26If the ``devno`` property is not specified for a device, QEMU will choose the
     27next free device number in subchannel set 0, skipping to the next subchannel
     28set if no more device numbers are free.
     29
     30QEMU places a device at the first free subchannel in the specified subchannel
     31set. If a device is hotunplugged and later replugged, it may appear at a
     32different subchannel. (This is similar to how z/VM works.)
     33
     34
     35Examples
     36--------
     37
     38* a virtio-net device, cssid/ssid/devno automatically assigned::
     39
     40    -device virtio-net-ccw
     41
     42  In a Linux guest (without default devices and no other devices specified
     43  prior to this one), this will show up as ``0.0.0000`` under subchannel
     44  ``0.0.0000``.
     45
     46  The auto-assigned-properties in QEMU (as seen via e.g. ``info qtree``)
     47  would be ``dev_id = "fe.0.0000"`` and ``subch_id = "fe.0.0000"``.
     48
     49* a virtio-rng device in subchannel set ``0``::
     50
     51    -device virtio-rng-ccw,devno=fe.0.0042
     52
     53  If added to the same Linux guest as above, it would show up as ``0.0.0042``
     54  under subchannel ``0.0.0001``.
     55
     56  The properties for the device would be ``dev_id = "fe.0.0042"`` and
     57  ``subch_id = "fe.0.0001"``.
     58
     59* a virtio-gpu device in subchannel set ``2``::
     60
     61    -device virtio-gpu-ccw,devno=fe.2.1111
     62
     63  If added to the same Linux guest as above, it would show up as ``0.2.1111``
     64  under subchannel ``0.2.0000``.
     65
     66  The properties for the device would be ``dev_id = "fe.2.1111"`` and
     67  ``subch_id = "fe.2.0000"``.
     68
     69* a virtio-mouse device in a non-standard channel subsystem image::
     70
     71    -device virtio-mouse-ccw,devno=2.0.2222
     72
     73  This would not show up in a standard Linux guest.
     74
     75  The properties for the device would be ``dev_id = "2.0.2222"`` and
     76  ``subch_id = "2.0.0000"``.
     77
     78* a virtio-keyboard device in another non-standard channel subsystem image::
     79
     80    -device virtio-keyboard-ccw,devno=0.0.1234
     81
     82  This would not show up in a standard Linux guest, either, as ``0`` is not
     83  the standard channel subsystem image id.
     84
     85  The properties for the device would be ``dev_id = "0.0.1234"`` and
     86  ``subch_id = "0.0.0000"``.