On Tue, 27 Nov 2018, Lendacky, Thomas wrote: > On 11/25/2018 12:33 PM, Thomas Gleixner wrote: > > --- a/arch/x86/kernel/process.c > > +++ b/arch/x86/kernel/process.c > > @@ -406,6 +406,11 @@ static __always_inline void spec_ctrl_up > > if (static_cpu_has(X86_FEATURE_SSBD)) > > msr |= ssbd_tif_to_spec_ctrl(tifn); > > I did some quick testing and found my original logic was flawed. Since > spec_ctrl_update_msr() can now be called for STIBP, an additional check > is needed to set the SSBD MSR bit. > > Both X86_FEATURE_VIRT_SSBD and X86_FEATURE_LS_CFG_SSBD cause > X86_FEATURE_SSBD to be set. Before this patch, spec_ctrl_update_msr() was > only called if X86_FEATURE_SSBD was set and one of the other SSBD features > wasn't set. But now, STIBP can cause spec_ctrl_update_msr() to get called > and cause the SSBD MSR bit to be set when it shouldn't (could result in > a GP fault).
The below should fix that. We have the same logic in x86_virt_spec_ctrl() Thanks, tglx 8<--------------- --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -403,10 +403,11 @@ static __always_inline void spec_ctrl_up u64 msr = x86_spec_ctrl_base; /* - * If X86_FEATURE_SSBD is not set, the SSBD bit is not to be - * touched. + * If SSBD is not controlled in MSR_SPEC_CTRL, the SSBD bit has not + * to be touched. */ - if (static_cpu_has(X86_FEATURE_SSBD)) + if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) || + static_cpu_has(X86_FEATURE_AMD_SSBD)) msr |= ssbd_tif_to_spec_ctrl(tifn); /* Only evaluate if conditional STIBP is enabled */