bool __read_mostly eager_page_split = true;
module_param(eager_page_split, bool, 0644);
+/* Enable/disable SMT_RSB bug mitigation */
+bool __read_mostly mitigate_smt_rsb;
+module_param(mitigate_smt_rsb, bool, 0444);
+
/*
* Restoring the host value for MSRs that are only consumed when running in
* usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU
r = KVM_CLOCK_VALID_FLAGS;
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,
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:
static int __init kvm_x86_init(void)
{
kvm_mmu_x86_module_init();
+ mitigate_smt_rsb &= boot_cpu_has_bug(X86_BUG_SMT_RSB) && cpu_smt_possible();
return 0;
}
module_init(kvm_x86_init);