Messages in this thread | | | From | "Lendacky, Thomas" <> | Subject | Re: [PATCH] x86/speculation: Add support for STIBP always-on preferred mode | Date | Tue, 11 Dec 2018 22:45:41 +0000 |
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On 12/11/2018 04:22 PM, Borislav Petkov wrote: > On Tue, Dec 11, 2018 at 10:17:30PM +0000, Lendacky, Thomas wrote: >> If using just SPECTRE_V2_USER_STRICT then the code in stibp_state() would >> have to be able differentiate between the case where the mode was switched >> because of X86_FEATURE_AMD_STIBP_ALWAYS_ON vs a kernel command line with >> "spectre_v2_user=on". I could always set and use a static variable in the >> file just for the stibp_state() case. > > Does it matter on X86_FEATURE_AMD_STIBP_ALWAYS_ON CPUs? > > I mean, we want STIBP to be always on there so you can do: > > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > index 25e914f77bb8..d14860d1cf9c 100644 > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -1089,7 +1089,10 @@ static char *stibp_state(void) > case SPECTRE_V2_USER_NONE: > return ", STIBP: disabled"; > case SPECTRE_V2_USER_STRICT: > - return ", STIBP: forced"; > + if (boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON)) > + return ", STIBP: always on"; > + else > + return ", STIBP: forced"; > case SPECTRE_V2_USER_PRCTL: > case SPECTRE_V2_USER_SECCOMP: > if (static_key_enabled(&switch_to_cond_stibp)) > > so if user has booted with spectre_v2_user=on, we say, "oh well, it is always > enabled anyway"... or?
I'm ok with that. Having said that, we can probably just leave it as is and return "forced" even for the ALWAYS_ON case, then.
But if we want to differentiate, though, a simple static bool that is set when the mode is switched works just as well.
> >> I'll give it a bit of time and see if there's any other discussion and >> re-submit without the new SPECTRE_V2_USER_STRICT_PREFERRED value. > > Sure.
Eh, I'll just submit v2 with the changes now and we can decide between the above or the bool.
Thanks, Tom
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