No. That would be the ideal situation, but it is not possible to make the CPU do that just from a microcode update, it would require new hardware. So we're left with creating other ways to get around it via software. The perf hit comes from those software fixes.
Meltdown is the most expensive perf wise, but more straight forward to fix. Processes can only access addresses mapped in their address space, so if you in unmap the kernel while a user process is running then they can't read it. This is expensive because every syscall now flushes the TLB due to changing the page table, so page accesses are in general slower.
Spectre is more complicated to fix. One part of the fix is the retpoline hack that basically attempts to defeat the branch predictor through clever code. It looks like the CPUs are also getting microcode update to allow it to disable the branch predictor in some situations.
