@@ -168,6 +168,10 @@ struct kvm_shared_msrs_global {
u32 msrs[KVM_NR_SHARED_MSRS];
};
+/* Enable/disable SMT_RSB bug mitigation */
+bool __read_mostly mitigate_smt_rsb;
+module_param(mitigate_smt_rsb, bool, 0444);
+
struct kvm_shared_msrs {
struct user_return_notifier urn;
bool registered;
@@ -3344,10 +3348,15 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = KVM_CLOCK_TSC_STABLE;
break;
case KVM_CAP_X86_DISABLE_EXITS:
- r |= KVM_X86_DISABLE_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
- KVM_X86_DISABLE_EXITS_CSTATE;
- if(kvm_can_mwait_in_guest())
- r |= KVM_X86_DISABLE_EXITS_MWAIT;
+ r = KVM_X86_DISABLE_EXITS_PAUSE;
+
+ if (!mitigate_smt_rsb) {
+ r |= KVM_X86_DISABLE_EXITS_HLT |
+ KVM_X86_DISABLE_EXITS_CSTATE;
+
+ if (kvm_can_mwait_in_guest())
+ r |= KVM_X86_DISABLE_EXITS_MWAIT;
+ }
break;
case KVM_CAP_X86_SMM:
/* SMBASE is usually relocated above 1M on modern chipsets,
@@ -4892,15 +4901,26 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
if (cap->args[0] & ~KVM_X86_DISABLE_VALID_EXITS)
break;
- if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&
- kvm_can_mwait_in_guest())
- kvm->arch.mwait_in_guest = true;
- if (cap->args[0] & KVM_X86_DISABLE_EXITS_HLT)
- kvm->arch.hlt_in_guest = true;
if (cap->args[0] & KVM_X86_DISABLE_EXITS_PAUSE)
kvm->arch.pause_in_guest = true;
- if (cap->args[0] & KVM_X86_DISABLE_EXITS_CSTATE)
- kvm->arch.cstate_in_guest = true;
+
+#define SMT_RSB_MSG "This processor is affected by the Cross-Thread Return Predictions vulnerability. " \
+ "KVM_CAP_X86_DISABLE_EXITS should only be used with SMT disabled or trusted guests."
+
+ if (!mitigate_smt_rsb) {
+ if (boot_cpu_has_bug(X86_BUG_SMT_RSB) && cpu_smt_possible() &&
+ (cap->args[0] & ~KVM_X86_DISABLE_EXITS_PAUSE))
+ pr_warn_once(SMT_RSB_MSG);
+
+ if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&
+ kvm_can_mwait_in_guest())
+ kvm->arch.mwait_in_guest = true;
+ if (cap->args[0] & KVM_X86_DISABLE_EXITS_HLT)
+ kvm->arch.hlt_in_guest = true;
+ if (cap->args[0] & KVM_X86_DISABLE_EXITS_CSTATE)
+ kvm->arch.cstate_in_guest = true;
+ }
+
r = 0;
break;
case KVM_CAP_MSR_PLATFORM_INFO:
@@ -7337,6 +7357,8 @@ int kvm_arch_init(void *opaque)
if (r)
goto out_free_percpu;
+ mitigate_smt_rsb &= boot_cpu_has_bug(X86_BUG_SMT_RSB) && cpu_smt_possible();
+
kvm_x86_ops = ops;
kvm_mmu_set_mask_ptes(PT_USER_MASK, PT_ACCESSED_MASK,