On 10/26/2018 09:58 AM, Waiman Long wrote: > 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. >
We're close to running out of the feature bits. So I'm trying not to use those. Tim
