On Fri, 2018-01-26 at 22:52 +0100, Borislav Petkov wrote: > On Fri, Jan 26, 2018 at 03:06:20PM -0600, Tom Lendacky wrote: > > > > So I like the idea of AMD_IBRS/AMD_IBPB/AMD_STIBP and then use the magic > > quotes as appropriate. We could probably use the magic quotes on > > AMD_STIBP and set X86_FEATURE_STIBP when we see X86_FEATURE_AMD_STIBP. > Like this? > > We set the respective Intel features when we detect the AMD ones so that > we get correct /proc/cpuinfo strings. The respective AMD ones are not > shown. > > + > + if (cpu_has(c, X86_FEATURE_AMD_IBRS)) > + set_cpu_cap(c, X86_FEATURE_IBRS); No, there is no X86_FEATURE_IBRS; that was going to be the "we are using IBRS" soft feature, analogous to X86_FEATURE_RETPOLINE and X86_FEATURE_IBPB, actually used for the alternatives. Intel doesn't *have* a feature bit for only IBRS. They have the bit which indicates that *both* the SPEC_CTRL (with IBRS) and PRED_CMD (with IBPB) registers are present. If we wanted to do this kind of thing, we'd do it the other way round. Turn the *Intel* feature into both 'IBRS' and 'IBPB' CPU-visible features, and have those defined in the AMD word. Then use virtual bits with "" for the software features, since we don't want *those* to appear in /proc/cpuinfo. I'll take a look at this in the morning.
Attachment:
smime.p7s
Description: S/MIME cryptographic signature
|