By now you’ve probably heard of the Meltdown/Spectre attacks. (background rumors, technical note) Matthew Dillon’s put together a Meltdown mitigation in DragonFly, done in four commits.

It’s turned off and on by the sysctl machdep.isolated_user_pmap – and defaults to on for Intel CPUs. Buildworld tests show about a 4-5% performance hit, but that’s only one form of activity, measured, so there will surely be other effects.

Note that Spectre is not mitigated by this commit series, and as I understand it, cannot be realistically fixed in software.

Update: Matthew Dillon posted a summary to users@.

Update 2: He told us so.