RHBA-2010:0479 - Bug Fix Advisory

Topic

Updated kvm packages that address 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 packages fix the following bugs:

• it was found that qemu-img rebase could corrupt output images under

certain conditions, due to clusters being taken from the backing file
rather than the COW file. qemu-image rebase now always gives clusters in
the COW file priority over those in the backing file, resolving this issue.
(BZ#596378)

• for particular workloads, KVM would become stuck in an infinite loop

while updating a guest page table entry (PTE). The qemu process used by
qemu-kvm could not be killed, but continues to consume resources. This
issue has been resolved. (BZ#596381)

• a rare theoretical race condition was found in the pvclock code for

setting the wallclock. An unprotected global variable was used to hold
version data, allowing guests to interfere with one another if they would
both write wallclock data at the same time. The race condition has been
removed, and this issue is now resolved. (BZ#596625)

• an error in a rarely used code path in the refcount table growth code of

qcow2 caused inconsistencies in the metadata, which could lead to real data
corruption later on. The corruption after refblock allocation was fixed,
and this issue is now resolved. (BZ#602363)

• after saving a guest snapshot and restarting it, guests failed to boot

and suffered a kernel panic. This issue only occurred when guests used
virtio block drivers and ran multiple requests at the same time. The qcow2
block driver lacked a synchronous version, which has been added, and the
issue is now resolved. (BZ#604188)

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 - 596378 - After re-base snapshot, the file in the snapshot disappeared
• BZ - 596381 - kvm spinning updating a guest pte, unkillable
• BZ - 596625 - race condition in pvclock wallclock calculation
• BZ - 602363 - qcow2 corruption bug in refcount table growth
• BZ - 604188 - Guest suffers kernel panic when save snapshot then restart guest

CVEs

(none)

References

(none)