Messages in this thread | ![/](/images/icornerl.gif) | | From | "Lendacky, Thomas" <> | Subject | Re: [PATCH v2] x86/speculation: Add support for STIBP always-on preferred mode | Date | Wed, 12 Dec 2018 14:03:56 +0000 |
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On 12/11/2018 09:37 PM, Thomas Gleixner wrote: > On Wed, 12 Dec 2018, Borislav Petkov wrote: >> On Tue, Dec 11, 2018 at 10:46:16PM +0000, Lendacky, Thomas wrote: >>> + /* >>> + * At this point, an STIBP mode other than "off" has been set. >>> + * If STIBP support is not being forced, check if STIBP always-on >>> + * is preferred. >>> + */ >>> + if (mode != SPECTRE_V2_USER_STRICT && >>> + boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON)) { >>> + stibp_always_on = true; >>> + mode = SPECTRE_V2_USER_STRICT; >>> + pr_info("mitigation: STIBP always-on is preferred\n"); >>> + } >>> + >>> /* Initialize Indirect Branch Prediction Barrier */ >>> if (boot_cpu_has(X86_FEATURE_IBPB)) { >>> setup_force_cpu_cap(X86_FEATURE_USE_IBPB); >>> @@ -1088,7 +1102,8 @@ static char *stibp_state(void) >>> case SPECTRE_V2_USER_NONE: >>> return ", STIBP: disabled"; >>> case SPECTRE_V2_USER_STRICT: >>> - return ", STIBP: forced"; >>> + return stibp_always_on ? ", STIBP: always-on" >>> + : ", STIBP: forced"; >> >> I still don't like that separate stibp_always_on variable when we can do >> all the querying just by using mode and X86_FEATURE_AMD_STIBP_ALWAYS_ON. > > Hmmm. I've not seen the V1 of this (it's not in my inbox) but the v1->v2 > changes contain:
That's strange, you were on the cc: list. Anyway, here's a link to the first version: https://lkml.org/lkml/2018/12/11/1248
> >>> - Removed explicit SPECTRE_V2_USER_STRICT_PREFERRED mode > > Now I really have to ask why? > > Neither the extra variable nor the cpu feature check are pretty. An > explicit mode is way better in terms of code clarity and you get the proper > printout via spectre_v2_user_strings. > > Hmm?
That is what the first version did. See if that's in-line with what you're thinking.
Thanks, Tom
> > tglx >
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