The following commit has been merged into the x86/bugs branch of tip: Commit-ID: 80dacb080461edfc1d854721ee6933a4cfa3b602 Gitweb: https://git.kernel.org/tip/80dacb080461edfc1d854721ee6933a4cfa3b602 Author: Yosry Ahmed <yosry.ahmed@xxxxxxxxx> AuthorDate: Thu, 27 Feb 2025 01:27:10 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Thu, 27 Feb 2025 10:57:20 +01:00 x86/bugs: Use a static branch to guard IBPB on vCPU switch Instead of using X86_FEATURE_USE_IBPB to guard the IBPB execution in KVM when a new vCPU is loaded, introduce a static branch, similar to switch_mm_*_ibpb. This makes it obvious in spectre_v2_user_select_mitigation() what exactly is being toggled, instead of the unclear X86_FEATURE_USE_IBPB (which will be shortly removed). It also provides more fine-grained control, making it simpler to change/add paths that control the IBPB in the vCPU switch path without affecting other IBPBs. Signed-off-by: Yosry Ahmed <yosry.ahmed@xxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Acked-by: Sean Christopherson <seanjc@xxxxxxxxxx> Link: https://lore.kernel.org/r/20250227012712.3193063-5-yosry.ahmed@xxxxxxxxx --- arch/x86/include/asm/nospec-branch.h | 2 ++ arch/x86/kernel/cpu/bugs.c | 5 +++++ arch/x86/kvm/svm/svm.c | 2 +- arch/x86/kvm/vmx/vmx.c | 2 +- 4 files changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 7cbb76a..36bc395 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -552,6 +552,8 @@ DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp); DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb); +DECLARE_STATIC_KEY_FALSE(switch_vcpu_ibpb); + DECLARE_STATIC_KEY_FALSE(mds_idle_clear); DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush); diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 1d7afc4..7f904d0 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -113,6 +113,10 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); /* Control unconditional IBPB in switch_mm() */ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb); +/* Control IBPB on vCPU load */ +DEFINE_STATIC_KEY_FALSE(switch_vcpu_ibpb); +EXPORT_SYMBOL_GPL(switch_vcpu_ibpb); + /* Control MDS CPU buffer clear before idling (halt, mwait) */ DEFINE_STATIC_KEY_FALSE(mds_idle_clear); EXPORT_SYMBOL_GPL(mds_idle_clear); @@ -1365,6 +1369,7 @@ spectre_v2_user_select_mitigation(void) /* Initialize Indirect Branch Prediction Barrier */ if (boot_cpu_has(X86_FEATURE_IBPB)) { setup_force_cpu_cap(X86_FEATURE_USE_IBPB); + static_branch_enable(&switch_vcpu_ibpb); spectre_v2_user_ibpb = mode; switch (cmd) { diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 57222c3..a73875f 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1566,7 +1566,7 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu) sd->current_vmcb = svm->vmcb; if (!cpu_feature_enabled(X86_FEATURE_IBPB_ON_VMEXIT) && - cpu_feature_enabled(X86_FEATURE_USE_IBPB)) + static_branch_likely(&switch_vcpu_ibpb)) indirect_branch_prediction_barrier(); } if (kvm_vcpu_apicv_active(vcpu)) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 042b7a8..956f914 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1477,7 +1477,7 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, * performs IBPB on nested VM-Exit (a single nested transition * may switch the active VMCS multiple times). */ - if (cpu_feature_enabled(X86_FEATURE_USE_IBPB) && + if (static_branch_likely(&switch_vcpu_ibpb) && (!buddy || WARN_ON_ONCE(buddy->vmcs != prev))) indirect_branch_prediction_barrier(); }
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