> > AND K5 speculates, Cyrix 6x86 speculates, IDT WinChip does not. I think > > this should be > > > > X86_VENDOR_ANY, 4 > > X86_VENDOR_INTEL, 5, > > X86_VENDOR_CENTAUR, 5, > > Hm, for the specific case of controlling X86_BUG_CPU_MELTDOWN it's not > just "speculates" which is the criterion. It's "optimises away the > permissions checks while speculating, on the assumption that it'll be > fixed up before retiring the instruction".
Nobody has published official statements on Cyrix or AMD 32bit processors so we don't know if they are vulnerable to meltdown. One problem I suspect is that as with things like Alpha 21264 - the people who knew are probably long retired. We do know the Intel ones I listed are OK and the Centaur. If someone can figure out the Cyrix and AMD cases that would be great. > By the time the dust settles we might end up with a bunch of different > match tables, *one* of which is "does not speculate at all". And the > conditions for the different bugs will each use different sets of match > tables. For example > > if (!x86_match_cpu(cpu_no_speculation_at_all) && > !x86_match_cpu(speculation_but_no_meltdown) && > !cpu_sets_rdcl_no()) > setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN); > > if (!x86_match_cpu(cpu_no_speculation_at_all) && > !x86_match_cpu(no_branch_target_buffer)) > setup_force_cpu_bug(X86_BUG_SPECTRE_V2); There are afaik no x86 processors that speculate and don't have a BTB. It's a bit like building a racing car with no gearbox. Alan
