Meltdown/Spectre mitigation for 4.15 and beyond
Meltdown/Spectre mitigation for 4.15 and beyond
Posted Jan 17, 2018 11:08 UTC (Wed) by dwmw2 (subscriber, #2063)In reply to: Meltdown/Spectre mitigation for 4.15 and beyond by paulj
Parent article: Meltdown/Spectre mitigation for 4.15 and beyond
Intel documentation is here. I haven't seen public AMD documentation yet (they have IBPB but not IBRS).
No, it isn't just disabling branch prediction completely. I think that what they could achieve in the microcode hacks was fairly limited. So in some ways setting IBRS is a partial barrier, and flushes certain predictions from the store. But leaving IBRS set also makes things go slow, which implies that it's doing some checking at all times. The details are opaque and will vary from generation to generation.
Thankfully we don't really need IBRS except on Skylake (where it doesn't suck quite so much anyway).
Posted Jan 19, 2018 12:43 UTC (Fri)
by anton (subscriber, #25547)
[Link]
Unfortunately, the Intel documentation is quite abstract. It does not tell us what these things actually do (probably because that's different for different generations); instead it tries to specify how to use them and/or what guarantees these things give (but even that is not very clear).
Meltdown/Spectre mitigation for 4.15 and beyond