[zimmerfrei]

In the simplest Meltdown case, the offending instruction is really executed and a General Protection Fault occurs. That is handled in the kernel which at that point could (simply?) flush all caches to remove the leaked information.

The real problem with Meltdown seems to occur when: 1) The offending instruction is NOT really executed because it is in a branch which is not actually taken. 2) The offending instruction is executed but within a transaction, which leads to an exception-free rollback (with leaked information left in cache though).

AFAIK neither is (or can be made) visible to the kernel (which could explain the very large PTI patch), but I do wonder if they are events that can be hanlded at the microcode level, in which case a microcode update from Intel could mitigate them.