On 10/17/2018 01:59 PM, Tim Chen wrote: > Add static key to indicate whether we are using Enhanced IBRS to mitigate > Spectre v2. This will be used in later patches to disengage STIBP code > for Spectre v2 mitigation as STIBP is not needed when Enhanced IBRS is > in use. > > Signed-off-by: Tim Chen <[email protected]> > --- > arch/x86/include/asm/nospec-branch.h | 3 +++ > arch/x86/kernel/cpu/bugs.c | 4 ++++ > 2 files changed, 7 insertions(+) > > diff --git a/arch/x86/include/asm/nospec-branch.h > b/arch/x86/include/asm/nospec-branch.h > index fd2a8c1..d57e84e 100644 > --- a/arch/x86/include/asm/nospec-branch.h > +++ b/arch/x86/include/asm/nospec-branch.h > @@ -3,6 +3,7 @@ > #ifndef _ASM_X86_NOSPEC_BRANCH_H_ > #define _ASM_X86_NOSPEC_BRANCH_H_ > > +#include <linux/static_key.h> > #include <asm/alternative.h> > #include <asm/alternative-asm.h> > #include <asm/cpufeatures.h> > @@ -228,6 +229,8 @@ enum ssb_mitigation { > extern char __indirect_thunk_start[]; > extern char __indirect_thunk_end[]; > > +DECLARE_STATIC_KEY_FALSE(spectre_v2_enhanced_ibrs); > + > /* > * On VMEXIT we must ensure that no RSB predictions learned in the guest > * can be followed in the host, by overwriting the RSB completely. Both > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > index b2f6b8b..2fc7b4e 100644 > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -142,6 +142,9 @@ static const char *spectre_v2_strings[] = { > [SPECTRE_V2_IBRS_ENHANCED] = "Mitigation: Enhanced IBRS", > }; > > +DEFINE_STATIC_KEY_FALSE(spectre_v2_enhanced_ibrs); > +EXPORT_SYMBOL(spectre_v2_enhanced_ibrs); > + > #undef pr_fmt > #define pr_fmt(fmt) "Spectre V2 : " fmt > > @@ -386,6 +389,7 @@ static void __init spectre_v2_select_mitigation(void) > /* Force it so VMEXIT will restore correctly */ > x86_spec_ctrl_base |= SPEC_CTRL_IBRS; > wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); > + static_branch_enable(&spectre_v2_enhanced_ibrs); > goto specv2_set_mode; > } > if (IS_ENABLED(CONFIG_RETPOLINE))
Why you need a static key for enhanced IBRS? It is supposed to be set at boot time and never get changed after that. It will be easier to use a feature bit for that instead. We usually use static key when the value can be changed at run time. Cheers, Longman
