Years ago, in school, my professor said that the cost of clearing the page table on context switches killed performance on minix (and microkernels in general)

Years ago, in school, my professor said that the cost of clearing the page table on context switches killed performance on minix (and microkernels in general) Given that Linux is now implementing certain mitigations against memory side channels, is the performance gain lost? I assume Linux now clears the page table when switching between kernel and user mode? Perhaps obviously, I don't know many details on this stuff, I'm curious if others know more?