Meltdown and Spectre mitigations — a February update [LWN.net]

Meltdown and Spectre mitigations — a February update

Posted Feb 6, 2018 16:53 UTC (Tue) by corsac (subscriber, #49696)
In reply to: Meltdown and Spectre mitigations — a February update by corbet
Parent article: Meltdown and Spectre mitigations — a February update

But future processors with RDCL_NO (protection against Meltdown) are likely to have SMEP/SMAP support.

And past processors without SMEP are unlikely to have PCID, so the cost of KPTI is huge there.

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Meltdown and Spectre mitigations — a February update

Posted Feb 7, 2018 15:19 UTC (Wed) by MarcB (subscriber, #101804) [Link] (1 responses)

The cost is fixed per syscall. So it is marginal for many workloads, even on old CPUs. And, of course, horrible for others, even on modern CPUs.

I am wondering, if it would be possible to lower the cost significantly. There are architectures - like SPARC - where separate address spaces are mandatory, after all. Did they accept the performance penalty or have they put thought - and silicone - into optimizing this? (Likely: both).

From a layman's view, separate address spaces seem like the "cleaner" solution.

Meltdown and Spectre mitigations — a February update

Posted Feb 7, 2018 15:21 UTC (Wed) by MarcB (subscriber, #101804) [Link]

I'd like to retract an 'e' :-)