Red Hat ENTERPRISE LINUX 5.5 - TECHNICAL NOTES Manual page 321

• When using Single Root I/O Virtualization (SR-IOV) devices under Xen, a single Hardware Virtual
Machine (HVM) guest is limited to 12 Virtual Function (VF) assignments.
• When booting a fully virtualized Xen guest, the following message may be displayed on the guest
console:
testing NMI watchdog -... <4>
WARNING: CPU#0: NMI appears to be stuck (0->0)!
This issue is caused by an implementation issue with the Xen hypervisor and can be safely ignored.
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(BZ#500845)
• Diskette drive media will not be accessible when using the virtualized kernel. To work around this,
use a USB-attached diskette drive instead.
Note that diskette drive media works well with other non-virtualized kernels.
• Formatting a disk when running Windows 2008 or Windows Vista as a guest can crash when the
guest has been booted with multiple virtual CPUs. To work around this, boot the guest with a single
virtual CPU when formatting.
• Fully virtualized guests cannot correct for time lost due to the domain being paused and unpaused.
Being able to correctly track the time across pause and unpause events is one of the advantages
of paravirtualized kernels. This issue is being addressed upstream with replaceable timers, so
fully virtualized guests will have paravirtualized timers. Currently, this code is under development
upstream and should be available in later versions of Red Hat Enterprise Linux.
The following note applies to x86_64 Architectures:
• Upgrading a host (dom0) system to Red Hat Enterprise Linux 5.2 may render existing Red Hat
Enterprise Linux 4.5 SMP paravirtualized guests unbootable. This is more likely to occur when the
host system has more than 4GB of RAM.
To work around this, boot each Red Hat Enterprise Linux 4.5 guest in single CPU mode and
upgrade its kernel to the latest version (for Red Hat Enterprise Linux 4.5.z).
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BZ#251013)
The following note applies to the ia64 Architecture:
• On some Itanium systems configured for console output to VGA, the dom0 virtualized kernel may
fail to boot. This is because the virtualized kernel failed to properly detect the default console device
from the Extensible Firmware Interface (EFI) settings.
When this occurs, add the boot parameter console=tty to the kernel boot options in /boot/efi/
(BZ#249076)
elilo.conf.
• On some Itanium systems (such as the Hitachi Cold Fusion 3e), the serial port cannot be detected
in dom0 when VGA is enabled by the EFI Maintenance Manager. As such, you need to supply the
following serial port information to the dom0 kernel:
• Speed in bits/second
• Number of data bits
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(BZ#441627)
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kernel-xen
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(BZ#511403)
48
(BZ#401081)
50
(BZ#422531)
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(BZ#253087
,
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