Wired Xen error

I was trying to migrate a VM from an older version of Xen to Xen 4.6. The console did not work after boot, it showed the login prompt, but it was not possible to type. I saw these error messages:

[ 24.684852] genirq: Flags mismatch irq 8. 00000000 (hvc_console) vs. 00000000 (rtc0)
[ 24.684860] hvc_open: request_irq failed with rc -16.

In hvc console not working on 4.4.0 guest I found the workaround to set 2 vpus for the VM. This worked.