RHBA-2010:0536 - Bug Fix Advisory

Topic

Updated kvm packages that resolve several issues are now available.

Description

KVM (Kernel-based Virtual Machine) is a full virtualization solution for Linux
on AMD64 and Intel 64 systems. KVM is a Linux kernel module built for the
standard Red Hat Enterprise Linux kernel. KVM can run multiple unmodified,
virtualized guest Windows and Linux operating systems.

These updated kvm packages provide fixes for the following bugs:

• the virtio-blk back end for qemu-kvm performed unnecessary zeroing of memory

on every I/O request, which reduced virtual guest performance. With this update,
the virtio-blk back end avoids spurious zeroing of request structures on each
I/O request, with the result that guest performance is increased. (BZ#604159)

• in the kvm kernel module, some internal KVM memory slots were incorrectly

being handled by copy-on-write after a fork() function call, which caused issues
when qemu-kvm ran child processes. This update fixes the handling of internal
KVM memory slots on fork() to avoid those issues. (BZ#610341)

• when using the Network File System (NFS), lseek(SEEK_END) operations resulted

in a GETATTR command being sent to th eserver, with the result that performance
was reduced on disk images over NFS. With this update, the pread() and pwrite()
functions are used instead of lseek(), read() and write(), with the result that
performance is increased when using NFS. (BZ#610344)

• following writing metadata to a QCOW2 disk image, metadata was not flushed,

which could have potentially caused the disk image to become corrupted in the
event of system disruption (such as a power outage). With this update, metadata
is flushed after being written, thus increasing QCOW2 image integrity, and
decreasing the likelihood of image corruption. (BZ#612507)

• when using QCOW2 disk images, certain I/O operation or disk space depletion

errors could potentially have caused image corruption or a virtual guest to stop
running. This was due to the improper error-handling code for QCOW2 disk images.
This has been fixed with this update so that the aforementioned types of errors
are handled correctly, thus increasing QCOW2 disk integrity in such situations.
(BZ#612508)

All KVM users should upgrade to these updated packages, which contain backported
patches to resolve these issues.

Solution

Before applying this update, make sure all previously-released errata
relevant to your system have been applied.

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
http://kbase.redhat.com/faq/docs/DOC-11259

Affected Products

• Red Hat Enterprise Linux Server 5 x86_64
• Red Hat Enterprise Linux Workstation 5 x86_64

Fixes

• BZ - 604159 - virtio-blk: Avoid zeroing every request structure
• BZ - 610341 - fork causes trouble for vcpu threads
• BZ - 610344 - Excessive lseek() causes severe performance issues with vm disk images over NFS
• BZ - 612507 - qcow2 image corruption when using cache=writeback
• BZ - 612508 - Backport qcow2 fixes to RHEL 5

CVEs

(none)

References

(none)