Installation guide

Windows Server 2008
Windows 7
Windows Server 2012
Windows 8 (32/64 bit)
T h e p ara- virt u aliz ed clo ck
Guests using the Time Stamp Counter (TSC) as a clock source may suffer timing issues.
KVM works around hosts that do not have a constant Time Stamp Counter by providing
guests with a para-virtualized clock. Additionally, the para-virtualized clock assists with
time adjustments needed after a guest runs S3 or suspend to RAM operations.
T h e p ara- virt u aliz ed serial d evice ( virt io - serial)
The para-virtualized serial device is a bytestream-oriented, character stream device, and
provides a simple communication interface between the host's user space and the guest's
user space.
T h e b allo o n d evice ( virt io - b allo o n )
The balloon device can designate part of a virtual machine's RAM as not being used (a
process known as balloon inflation), so that the memory can be freed for the host (or for
other virtual machines on that host) to use. When the virtual machine needs the memory
again, the balloon can be deflated and the host can distribute the RAM back to the virtual
machine.
T h e p ara- virt u aliz ed g rap h ics card ( Q XL)
The para-virtualized graphics card works with the QXL driver to provide an efficient way to
display a virtual machine's graphics from a remote host. The QXL driver is required to use
SPICE.
4 .3.3. Physical host devices
Certain hardware platforms allow virtual machines to directly access various hardware devices and
components. This process in virtualization is known as device assignment. Device assignment is also
known as passthrough.
PCI d evice assig n men t
The KVM hypervisor supports attaching PCI devices on the host system to virtual machines.
PCI device assignment allows guests to have exclusive access to PCI devices for a range of
tasks. It allows PCI devices to appear and behave as if they were physically attached to the
guest virtual machine.
Device assignment is supported on PCI Express devices, with the exception of graphics
cards. Parallel PCI devices may be supported as assigned devices, but they have severe
limitations due to security and system configuration conflicts.
Note
For more information on device assignment, refer to the Red Hat Enterprise Linux 6
Virtualization Host Configuration and Guest Installation Guide.
Red Hat Ent erprise Linux 6 Virt ualizat io n G et t ing St art ed G uide
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