Function has_ibrs 

pub fn has_ibrs(
    cpuid: &impl Cpuid,
    msr: &impl ReadReg<ArchCapabilitiesMsr>,
    always_on_mode: bool,
) -> bool

Whether Indirect Branch Restricted Speculation (IBRS) is supported. The “always on” mode refers to an optimization in which IBRS need only be enabled once; IBRS in this mode are also referred to as “enhanced”.

https://software.intel.com/security-software-guidance/deep-dives/deep-dive-indirect-branch-restricted-speculation.