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    Subject[Patch v3 05/13] x86/smt: Create cpu_smt_enabled static key for SMT specific code
    Date
    Create the cpu_smt_enabled static key to indicate if we are
    using SMT. SMT specific code paths are executed only when SMT
    code paths are enabled by this key.

    Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
    ---
    arch/x86/kernel/cpu/bugs.c | 2 +-
    arch/x86/kvm/vmx.c | 2 +-
    include/linux/cpu.h | 1 +
    kernel/cpu.c | 12 ++++++++++--
    4 files changed, 13 insertions(+), 4 deletions(-)

    diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
    index 6ed82ea..0338fa1 100644
    --- a/arch/x86/kernel/cpu/bugs.c
    +++ b/arch/x86/kernel/cpu/bugs.c
    @@ -358,7 +358,7 @@ void arch_smt_update(void)

    mutex_lock(&spec_ctrl_mutex);
    mask = x86_spec_ctrl_base;
    - if (cpu_smt_control == CPU_SMT_ENABLED)
    + if (static_branch_likely(&cpu_smt_enabled))
    mask |= SPEC_CTRL_STIBP;
    else
    mask &= ~SPEC_CTRL_STIBP;
    diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
    index 533a327..8ec0ea3 100644
    --- a/arch/x86/kvm/vmx.c
    +++ b/arch/x86/kvm/vmx.c
    @@ -11072,7 +11072,7 @@ static int vmx_vm_init(struct kvm *kvm)
    * Warn upon starting the first VM in a potentially
    * insecure environment.
    */
    - if (cpu_smt_control == CPU_SMT_ENABLED)
    + if (static_branch_likely(&cpu_smt_enabled))
    pr_warn_once(L1TF_MSG_SMT);
    if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_NEVER)
    pr_warn_once(L1TF_MSG_L1D);
    diff --git a/include/linux/cpu.h b/include/linux/cpu.h
    index 218df7f..b54f085 100644
    --- a/include/linux/cpu.h
    +++ b/include/linux/cpu.h
    @@ -188,5 +188,6 @@ static inline void cpu_smt_disable(bool force) { }
    static inline void cpu_smt_check_topology_early(void) { }
    static inline void cpu_smt_check_topology(void) { }
    #endif
    +DECLARE_STATIC_KEY_TRUE(cpu_smt_enabled);

    #endif /* _LINUX_CPU_H_ */
    diff --git a/kernel/cpu.c b/kernel/cpu.c
    index 3adecda..ad28afc 100644
    --- a/kernel/cpu.c
    +++ b/kernel/cpu.c
    @@ -349,6 +349,8 @@ EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
    #ifdef CONFIG_HOTPLUG_SMT
    enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
    EXPORT_SYMBOL_GPL(cpu_smt_control);
    +DEFINE_STATIC_KEY_TRUE(cpu_smt_enabled);
    +EXPORT_SYMBOL_GPL(cpu_smt_enabled);

    static bool cpu_smt_available __read_mostly;

    @@ -364,6 +366,7 @@ void __init cpu_smt_disable(bool force)
    } else {
    cpu_smt_control = CPU_SMT_DISABLED;
    }
    + static_branch_disable(&cpu_smt_enabled);
    }

    /*
    @@ -373,8 +376,10 @@ void __init cpu_smt_disable(bool force)
    */
    void __init cpu_smt_check_topology_early(void)
    {
    - if (!topology_smt_supported())
    + if (!topology_smt_supported()) {
    cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
    + static_branch_disable(&cpu_smt_enabled);
    + }
    }

    /*
    @@ -386,8 +391,10 @@ void __init cpu_smt_check_topology_early(void)
    */
    void __init cpu_smt_check_topology(void)
    {
    - if (!cpu_smt_available)
    + if (!cpu_smt_available) {
    cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
    + static_branch_disable(&cpu_smt_enabled);
    + }
    }

    static int __init smt_cmdline_disable(char *str)
    @@ -2072,6 +2079,7 @@ static int cpuhp_smt_enable(void)

    cpu_maps_update_begin();
    cpu_smt_control = CPU_SMT_ENABLED;
    + static_branch_enable(&cpu_smt_enabled);
    arch_smt_update();
    for_each_present_cpu(cpu) {
    /* Skip online CPUs and CPUs on offline nodes */
    --
    2.9.4
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