Chenyi Qiang <chenyi.qiang@xxxxxxxxx> writes: > Virtual Machine can exploit bus locks to degrade the performance of > system. Bus lock can be caused by split locked access to writeback(WB) > memory or by using locks on uncacheable(UC) memory. The bus lock is > typically >1000 cycles slower than an atomic operation within a cache > line. It also disrupts performance on other cores (which must wait for > the bus lock to be released before their memory operations can > complete). > > To address the threat, bus lock VM exit is introduced to notify the VMM > when a bus lock was acquired, allowing it to enforce throttling or other > policy based mitigations. > > A VMM can enable VM exit due to bus locks by setting a new "Bus Lock > Detection" VM-execution control(bit 30 of Secondary Processor-based VM > execution controls). If delivery of this VM exit was preempted by a > higher priority VM exit (e.g. EPT misconfiguration, EPT violation, APIC > access VM exit, APIC write VM exit, exception bitmap exiting), bit 26 of > exit reason in vmcs field is set to 1. > > In current implementation, the KVM exposes this capability through > KVM_CAP_X86_BLD. The user can set it to enable the bus lock VM exit > (disabled by default). If bus locks in guest are detected by KVM, exit > to user space even when current exit reason is handled by KVM > internally. Set a new field KVM_RUN_BUS_LOCK in vcpu->run->flags to > inform the user space that there is a bus lock in guest and it is > preempted by a higher priority VM exit. > > Every bus lock acquired in non-root mode will be recorded in > vcpu->stat.bus_locks and exposed through debugfs when the bus lock > VM exit is enabled. > > Document for Bus Lock VM exit is now available at the latest "Intel > Architecture Instruction Set Extensions Programming Reference". > > Document Link: > https://software.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html > > Co-developed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx> > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx> > Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx> > --- > arch/x86/include/asm/kvm_host.h | 9 ++++++++ > arch/x86/include/asm/vmx.h | 1 + > arch/x86/include/asm/vmxfeatures.h | 1 + > arch/x86/include/uapi/asm/kvm.h | 1 + > arch/x86/include/uapi/asm/vmx.h | 4 +++- > arch/x86/kvm/vmx/capabilities.h | 6 +++++ > arch/x86/kvm/vmx/vmx.c | 33 ++++++++++++++++++++++++++- > arch/x86/kvm/vmx/vmx.h | 2 +- > arch/x86/kvm/x86.c | 36 +++++++++++++++++++++++++++++- > arch/x86/kvm/x86.h | 5 +++++ > include/uapi/linux/kvm.h | 2 ++ > 11 files changed, 96 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index be5363b21540..bfabe2f15b30 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -829,6 +829,9 @@ struct kvm_vcpu_arch { > > /* AMD MSRC001_0015 Hardware Configuration */ > u64 msr_hwcr; > + > + /* Set when bus lock VM exit is preempted by a higher priority VM exit */ > + bool bus_lock_detected; > }; > > struct kvm_lpage_info { > @@ -1002,6 +1005,9 @@ struct kvm_arch { > bool guest_can_read_msr_platform_info; > bool exception_payload_enabled; > > + /* Set when bus lock vm exit is enabled by user */ > + bool bus_lock_exit; > + > struct kvm_pmu_event_filter *pmu_event_filter; > struct task_struct *nx_lpage_recovery_thread; > }; > @@ -1051,6 +1057,7 @@ struct kvm_vcpu_stat { > u64 req_event; > u64 halt_poll_success_ns; > u64 halt_poll_fail_ns; > + u64 bus_locks; > }; > > struct x86_instruction_info; > @@ -1388,6 +1395,8 @@ extern u8 kvm_tsc_scaling_ratio_frac_bits; > extern u64 kvm_max_tsc_scaling_ratio; > /* 1ull << kvm_tsc_scaling_ratio_frac_bits */ > extern u64 kvm_default_tsc_scaling_ratio; > +/* bus lock detection supported */ > +extern bool kvm_has_bus_lock_exit; > > extern u64 kvm_mce_cap_supported; > > diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h > index cd7de4b401fe..93a880bc31a7 100644 > --- a/arch/x86/include/asm/vmx.h > +++ b/arch/x86/include/asm/vmx.h > @@ -73,6 +73,7 @@ > #define SECONDARY_EXEC_PT_USE_GPA VMCS_CONTROL_BIT(PT_USE_GPA) > #define SECONDARY_EXEC_TSC_SCALING VMCS_CONTROL_BIT(TSC_SCALING) > #define SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE VMCS_CONTROL_BIT(USR_WAIT_PAUSE) > +#define SECONDARY_EXEC_BUS_LOCK_DETECTION VMCS_CONTROL_BIT(BUS_LOCK_DETECTION) > > #define PIN_BASED_EXT_INTR_MASK VMCS_CONTROL_BIT(INTR_EXITING) > #define PIN_BASED_NMI_EXITING VMCS_CONTROL_BIT(NMI_EXITING) > diff --git a/arch/x86/include/asm/vmxfeatures.h b/arch/x86/include/asm/vmxfeatures.h > index 9915990fd8cf..e80523346274 100644 > --- a/arch/x86/include/asm/vmxfeatures.h > +++ b/arch/x86/include/asm/vmxfeatures.h > @@ -83,5 +83,6 @@ > #define VMX_FEATURE_TSC_SCALING ( 2*32+ 25) /* Scale hardware TSC when read in guest */ > #define VMX_FEATURE_USR_WAIT_PAUSE ( 2*32+ 26) /* Enable TPAUSE, UMONITOR, UMWAIT in guest */ > #define VMX_FEATURE_ENCLV_EXITING ( 2*32+ 28) /* "" VM-Exit on ENCLV (leaf dependent) */ > +#define VMX_FEATURE_BUS_LOCK_DETECTION ( 2*32+ 30) /* VM-Exit when bus lock caused */ > > #endif /* _ASM_X86_VMXFEATURES_H */ > diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h > index 0780f97c1850..a1471c05f7f9 100644 > --- a/arch/x86/include/uapi/asm/kvm.h > +++ b/arch/x86/include/uapi/asm/kvm.h > @@ -111,6 +111,7 @@ struct kvm_ioapic_state { > #define KVM_NR_IRQCHIPS 3 > > #define KVM_RUN_X86_SMM (1 << 0) > +#define KVM_RUN_BUS_LOCK (1 << 1) > > /* for KVM_GET_REGS and KVM_SET_REGS */ > struct kvm_regs { > diff --git a/arch/x86/include/uapi/asm/vmx.h b/arch/x86/include/uapi/asm/vmx.h > index b8ff9e8ac0d5..14c177c4afd5 100644 > --- a/arch/x86/include/uapi/asm/vmx.h > +++ b/arch/x86/include/uapi/asm/vmx.h > @@ -88,6 +88,7 @@ > #define EXIT_REASON_XRSTORS 64 > #define EXIT_REASON_UMWAIT 67 > #define EXIT_REASON_TPAUSE 68 > +#define EXIT_REASON_BUS_LOCK 74 > > #define VMX_EXIT_REASONS \ > { EXIT_REASON_EXCEPTION_NMI, "EXCEPTION_NMI" }, \ > @@ -148,7 +149,8 @@ > { EXIT_REASON_XSAVES, "XSAVES" }, \ > { EXIT_REASON_XRSTORS, "XRSTORS" }, \ > { EXIT_REASON_UMWAIT, "UMWAIT" }, \ > - { EXIT_REASON_TPAUSE, "TPAUSE" } > + { EXIT_REASON_TPAUSE, "TPAUSE" }, \ > + { EXIT_REASON_BUS_LOCK, "BUS_LOCK" } > > #define VMX_EXIT_REASON_FLAGS \ > { VMX_EXIT_REASONS_FAILED_VMENTRY, "FAILED_VMENTRY" } > diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h > index 4bbd8b448d22..aa94535e6705 100644 > --- a/arch/x86/kvm/vmx/capabilities.h > +++ b/arch/x86/kvm/vmx/capabilities.h > @@ -262,6 +262,12 @@ static inline bool cpu_has_vmx_tsc_scaling(void) > SECONDARY_EXEC_TSC_SCALING; > } > > +static inline bool cpu_has_vmx_bus_lock_detection(void) > +{ > + return vmcs_config.cpu_based_2nd_exec_ctrl & > + SECONDARY_EXEC_BUS_LOCK_DETECTION; > +} > + > static inline bool cpu_has_vmx_apicv(void) > { > return cpu_has_vmx_apic_register_virt() && > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 89c131eaedf2..1560e51d2d8e 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -2460,7 +2460,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf, > SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE | > SECONDARY_EXEC_PT_USE_GPA | > SECONDARY_EXEC_PT_CONCEAL_VMX | > - SECONDARY_EXEC_ENABLE_VMFUNC; > + SECONDARY_EXEC_ENABLE_VMFUNC | > + SECONDARY_EXEC_BUS_LOCK_DETECTION; > if (cpu_has_sgx()) > opt2 |= SECONDARY_EXEC_ENCLS_EXITING; > if (adjust_vmx_controls(min2, opt2, > @@ -4247,6 +4248,9 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx) > } > } > > + if (!kvm_bus_lock_exit_enabled(vmx->vcpu.kvm)) > + exec_control &= ~SECONDARY_EXEC_BUS_LOCK_DETECTION; > + > vmx->secondary_exec_control = exec_control; > } > > @@ -5661,6 +5665,16 @@ static int handle_encls(struct kvm_vcpu *vcpu) > return 1; > } > > +static int handle_bus_lock(struct kvm_vcpu *vcpu) > +{ > + struct kvm_run *kvm_run = vcpu->run; > + > + vcpu->stat.bus_locks++; > + > + kvm_run->exit_reason = KVM_EXIT_BUS_LOCK; > + return 0; > +} > + > /* > * The exit handlers return 1 if the exit was handled fully and guest execution > * may resume. Otherwise they set the kvm_run parameter to indicate what needs > @@ -5717,6 +5731,7 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = { > [EXIT_REASON_VMFUNC] = handle_vmx_instruction, > [EXIT_REASON_PREEMPTION_TIMER] = handle_preemption_timer, > [EXIT_REASON_ENCLS] = handle_encls, > + [EXIT_REASON_BUS_LOCK] = handle_bus_lock, > }; > > static const int kvm_vmx_max_exit_handlers = > @@ -6809,6 +6824,19 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu) > if (unlikely(vmx->exit_reason.failed_vmentry)) > return EXIT_FASTPATH_NONE; > > + /* > + * check the exit_reason to see if there is a bus lock > + * happened in guest. > + */ > + if (kvm_bus_lock_exit_enabled(vmx->vcpu.kvm)) { > + if (vmx->exit_reason.bus_lock_detected) { > + vcpu->stat.bus_locks++; > + vcpu->arch.bus_lock_detected = true; > + } else { > + vcpu->arch.bus_lock_detected = false; This is a fast path so I'm wondering if we can move bus_lock_detected clearing somewhere else. > + } > + } > + > vmx->loaded_vmcs->launched = 1; > vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD); > > @@ -8060,6 +8088,9 @@ static __init int hardware_setup(void) > kvm_tsc_scaling_ratio_frac_bits = 48; > } > > + if (cpu_has_vmx_bus_lock_detection()) > + kvm_has_bus_lock_exit = true; > + > set_bit(0, vmx_vpid_bitmap); /* 0 is reserved for host */ > > if (enable_ept) > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h > index 06a91b224ef3..7e6d63a8589a 100644 > --- a/arch/x86/kvm/vmx/vmx.h > +++ b/arch/x86/kvm/vmx/vmx.h > @@ -104,7 +104,7 @@ union vmx_exit_reason { > u32 reserved23 : 1; > u32 reserved24 : 1; > u32 reserved25 : 1; > - u32 reserved26 : 1; > + u32 bus_lock_detected : 1; > u32 enclave_mode : 1; > u32 smi_pending_mtf : 1; > u32 smi_from_vmx_root : 1; > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 88c593f83b28..00a54d0cd7da 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -133,6 +133,8 @@ u64 __read_mostly kvm_max_tsc_scaling_ratio; > EXPORT_SYMBOL_GPL(kvm_max_tsc_scaling_ratio); > u64 __read_mostly kvm_default_tsc_scaling_ratio; > EXPORT_SYMBOL_GPL(kvm_default_tsc_scaling_ratio); > +bool __read_mostly kvm_has_bus_lock_exit; > +EXPORT_SYMBOL_GPL(kvm_has_bus_lock_exit); > > /* tsc tolerance in parts per million - default to 1/2 of the NTP threshold */ > static u32 __read_mostly tsc_tolerance_ppm = 250; > @@ -220,6 +222,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = { > VCPU_STAT("l1d_flush", l1d_flush), > VCPU_STAT("halt_poll_success_ns", halt_poll_success_ns), > VCPU_STAT("halt_poll_fail_ns", halt_poll_fail_ns), > + VCPU_STAT("bus_locks", bus_locks), > VM_STAT("mmu_shadow_zapped", mmu_shadow_zapped), > VM_STAT("mmu_pte_write", mmu_pte_write), > VM_STAT("mmu_pte_updated", mmu_pte_updated), > @@ -3538,6 +3541,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > case KVM_CAP_HYPERV_ENLIGHTENED_VMCS: > r = kvm_x86_ops.nested_ops->enable_evmcs != NULL; > break; > + case KVM_CAP_X86_BUS_LOCK_EXIT: > + r = kvm_has_bus_lock_exit; > + break; I think we can always report KVM_CAP_X86_BUS_LOCK_EXIT as supported (meaning KVM itself supports it) ... > default: > break; > } > @@ -4990,6 +4996,12 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, > kvm->arch.exception_payload_enabled = cap->args[0]; > r = 0; > break; > + case KVM_CAP_X86_BUS_LOCK_EXIT: > + if (!kvm_has_bus_lock_exit) > + return -EINVAL; ... because userspace can check for -EINVAL when enabling the cap. Or we can return e.g. -EOPNOTSUPP here. I don't have a strong opinion on the matter.. > + kvm->arch.bus_lock_exit = cap->args[0]; > + r = 0; > + break; > default: > r = -EINVAL; > break; > @@ -7732,12 +7744,23 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu) > struct kvm_run *kvm_run = vcpu->run; > > kvm_run->if_flag = (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0; > - kvm_run->flags = is_smm(vcpu) ? KVM_RUN_X86_SMM : 0; > kvm_run->cr8 = kvm_get_cr8(vcpu); > kvm_run->apic_base = kvm_get_apic_base(vcpu); > kvm_run->ready_for_interrupt_injection = > pic_in_kernel(vcpu->kvm) || > kvm_vcpu_ready_for_interrupt_injection(vcpu); > + > + if (is_smm(vcpu)) > + kvm_run->flags |= KVM_RUN_X86_SMM; > + else > + kvm_run->flags &= ~KVM_RUN_X86_SMM; > + > + if (vcpu->arch.bus_lock_detected && > + kvm_run->exit_reason != KVM_EXIT_BUS_LOCK) > + kvm_run->flags |= KVM_RUN_BUS_LOCK; > + else > + kvm_run->flags &= ~KVM_RUN_BUS_LOCK; > + > } > > static void update_cr8_intercept(struct kvm_vcpu *vcpu) > @@ -8597,6 +8620,17 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > kvm_lapic_sync_from_vapic(vcpu); > > r = kvm_x86_ops.handle_exit(vcpu, exit_fastpath); > + > + /* > + * Even when current exit reason is handled by KVM > + * internally, we still needs to exit to user space > + * when bus lock detected to inform that there is a > + * bus lock in guest. > + */ > + if (r > 0 && vcpu->arch.bus_lock_detected) { > + vcpu->run->exit_reason = KVM_EXIT_BUS_LOCK; > + r = 0; Can we maybe reset bus_lock_detected here? > + } > return r; > > cancel_injection: > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h > index 6eb62e97e59f..d3b1095cc8fb 100644 > --- a/arch/x86/kvm/x86.h > +++ b/arch/x86/kvm/x86.h > @@ -334,6 +334,11 @@ static inline bool kvm_cstate_in_guest(struct kvm *kvm) > return kvm->arch.cstate_in_guest; > } > > +static inline bool kvm_bus_lock_exit_enabled(struct kvm *kvm) > +{ > + return kvm->arch.bus_lock_exit; > +} > + > DECLARE_PER_CPU(struct kvm_vcpu *, current_vcpu); > > static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu) > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 4fdf30316582..e66aa4bdaf24 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -248,6 +248,7 @@ struct kvm_hyperv_exit { > #define KVM_EXIT_IOAPIC_EOI 26 > #define KVM_EXIT_HYPERV 27 > #define KVM_EXIT_ARM_NISV 28 > +#define KVM_EXIT_BUS_LOCK 29 > > /* For KVM_EXIT_INTERNAL_ERROR */ > /* Emulate instruction failed. */ > @@ -1031,6 +1032,7 @@ struct kvm_ppc_resize_hpt { > #define KVM_CAP_PPC_SECURE_GUEST 181 > #define KVM_CAP_HALT_POLL 182 > #define KVM_CAP_ASYNC_PF_INT 183 > +#define KVM_CAP_X86_BUS_LOCK_EXIT 184 > > #ifdef KVM_CAP_IRQ_ROUTING -- Vitaly
