temporary unresponsiveness or 'soft lockup' of KVM host and guest while a PCI device is being hot-plugged to the virtual machine

Solution Verified - Updated -


A KVM host and guest can appear to be unresponsive temporarily while a virtual PCI device such as virtio disk, virtio net, e1000 or rtl8139 is being hot-plugged to the virtual machine. If the duration of unresponsiveness exceeds the threshold of the 'soft lockup' watchdog, the host and guest kernel can log BUG: soft lockup ... events similar to the examples given under Diagostic Steps. If the KVM host is a node in a High Availability Cluster, it could even be evicted/fenced from the cluster.

This issue has originally been observed while a virtio disk was being hot-plugged to a large-sized virtual machine (16 virtual CPUs, 64 GB memory) that was running a cpu- and memory-intensive application. In that case the KVM host operating system was Red Hat Enterprise Linux 6.3 on a large-sized physical server (160 CPUs, ~1 TB memory), and the guest operating system was Red Hat Enterprise Linux 5.5.


  • Red Hat Enterprise Linux 6 based KVM host/hypervisor
  • Red Hat Enterprise Linux 5 or 6 guest
  • large sized virtual machine on large sized physical server

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