Seeing this on a few hosts and not sure why. VMs will suddenly just power off for no reason. Googling around provided some answers but none seem to resolve the issue. One of the servers this appears on is a relatively older server but I checked and it does support unrestricted mode and some of of the others are Dell R430/R730 class servers and absolutely support this.
Jun 16 21:23:04 server04 QEMU[2875]: KVM: entry failed, hardware error 0x80000021
Jun 16 21:23:04 server04 QEMU[2875]: If you're running a guest on an Intel machine without unrestricted mode
Jun 16 21:23:04 server04 QEMU[2875]: support, the failure can be most likely due to the guest entering an invalid
Jun 16 21:23:04 server04 QEMU[2875]: state for Intel VT. For example, the guest maybe running in big real mode
Jun 16 21:23:04 server04 QEMU[2875]: which is not supported on less recent Intel processors.