A single update for the TSC synchronixation sanity checks: The sad state of TSC being notoriously non-sychronized for several decades caused the kernel to grow quite rigorous sanity checks to detect whether the TSC is valid to be used for timekeeping. The TSC ADJUST MSR provides the offset between the initial TSC value after hardware reset and later modifications. This allows to detect cases where firmware tampers with the TSC and also allows to correct the firmware induced damage by resetting the offset in a controlled way. The universal correct rule is that the TSC ADJUST value has to be consistent within all CPUs of a socket. The kernel further assumes that the TSC offset should be consistent between sockets. That's not really correct as systems with a huge number of sockets are not architecurally guaranteed to reset the per socket TSC base synchronously. In case that the per socket offset is not consistent the kernel resets it to the offset of the boot CPU and then does a synchronization check which corrects for the inter socket delays. That works most of the time, but it is suboptimal as the firmware has eventually better information about the per socket offset and on sane systems that offset should just work in the validation checks.