Reportedly, adding pti=off to the kernel boot parameters will work around the issue for now.
Turning off pti in the guest kernel is done in any case for PV. The issue between 4.9.107 and 4.9.111 affects the detection and turning off of pti, that's why forcing it off helps. In 4.9.112 it's fixed in commit 1adc34adc3447c34926994b87db5d929f5ab45b5 "x86/cpu: Re-apply forced caps every time CPU caps are re-read" Hans
