CONFIG_CAVIUM_ERRATUM_30115 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm64

Cavium erratum 30115: Guest may disable interrupts in host

configname: CONFIG_CAVIUM_ERRATUM_30115

Linux Kernel Configuration
└─>Kernel Features
└─>ARM errata workarounds via the alternatives framework
└─>Cavium erratum 30115: Guest may disable interrupts in host
In linux kernel since version 4.2 (release Date: 2015-08-30)  
On ThunderX T88 pass 1.x through 2.2, T81 pass 1.0 through
1.2, and T83 Pass 1.0, KVM guest execution may disable
interrupts in host. Trapping both GICv3 group-0 and group-1
accesses sidesteps the issue.

If unsure, say Y.