This is a problem I've had on and off under CentOS5 and CentOS6, with both xen and kvm. Currently, it happens consistently with kvm on 6.5, e.g. with every kernel update. I *think* it generally worked fine with the 6.4 kernels.
There are 7 VMs running on a 6.5, x86_64, 8GB RAM host, each with 512MB RAM and using the e1000 NIC. I picked this specific NIC because the default does not allow reliable monitoring through SNMP (IIRC). The host has two bonded NICs with br0 running on top.
When the host reboots, the VMs will generally hang bringing up the virtual NIC, and I need to go through several iterations of destroy/create, for each VM, to get them running. The always hang here (copy&paste from console):
... Welcome to CentOS Starting udev: udev: starting version 147 piix4_smbus 0000:00:01.3: SMBus Host Controller at 0xb100, revision 0 e1000: Intel(R) PRO/1000 Network Driver - version 7.3.21-k8-NAPI e1000: Copyright (c) 1999-2006 Intel Corporation. ACPI: PCI Interrupt Link [LNKC] enabled at IRQ 11 e1000 0000:00:03.0: PCI INT A -> Link[LNKC] -> GSI 11 (level, high) -> IRQ 11 e1000 0000:00:03.0: eth0: (PCI:33MHz:32-bit) 00:16:3e:52:e3:0b e1000 0000:00:03.0: eth0: Intel(R) PRO/1000 Network Connection
Any suggestions on where to start looking?