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Date:   Fri, 11 Sep 2020 10:27:07 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Chenyi Qiang <chenyi.qiang@intel.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Xiaoyao Li <xiaoyao.li@intel.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC v3 2/2] KVM: VMX: Enable bus lock VM exit
Message-ID: <20200911172703.GE4344@sjchrist-ice>
References: <20200910083751.26686-1-chenyi.qiang@intel.com>
 <20200910083751.26686-3-chenyi.qiang@intel.com>
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On Thu, Sep 10, 2020 at 04:37:51PM +0800, Chenyi Qiang wrote:
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 5303dbc5c9bc..8059b8b21ecd 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -961,6 +961,9 @@ 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;

Maybe bus_lock_detection_enabled?  Then you don't need the comment or the
accessor.

> +
>  	struct kvm_pmu_event_filter *pmu_event_filter;
>  	struct task_struct *nx_lpage_recovery_thread;
>  };
> @@ -1347,6 +1350,8 @@ 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;

Hrm, it'd be nice to somehow squeeze this into kvm_cpu_caps, but I can't
think of a clever/clean way to do so.

>  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 adc59cf9036d..5dbfee639375 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2461,7 +2461,8 @@ 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,
> @@ -4244,6 +4245,9 @@ 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;
>  }
>  
> @@ -5685,6 +5689,14 @@ 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;
> +
> +	kvm_run->exit_reason = KVM_EXIT_BUS_LOCK;

No need for kvm_run, "vcpu->run->exit_reason = KVM_EXIT_BUS_LOCK" will do.

> +	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
> @@ -5741,6 +5753,7 @@ 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 =
> @@ -5979,7 +5992,7 @@ void dump_vmcs(void)
>   * The guest has exited.  See if we can fix it or if we need userspace
>   * assistance.
>   */
> -static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
> +static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  	union vmx_exit_reason exit_reason = vmx->exit_reason;
> @@ -6131,6 +6144,28 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>  	return 0;
>  }
>  
> +static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
> +{
> +	struct vcpu_vmx *vmx = to_vmx(vcpu);

Personal preference, but I'd probably skip the local 'vmx' variable since
there's only a single user, i.e. "to_vmx(vcpu)->exit_reason....".

> +	int ret = __vmx_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.

Run these lines out to the edge of 80 chars, wrapping this aggressively just
adds extra lines.

> +	 */
> +	if (vmx->exit_reason.bus_lock_detected) {
> +		if (ret > 0)
> +			vcpu->run->exit_reason = KVM_EXIT_BUS_LOCK;
> +		else
> +			vcpu->run->flags |= KVM_RUN_BUS_LOCK;
> +		return 0;
> +	}
> +	vcpu->run->flags &= ~KVM_RUN_BUS_LOCK;
> +	return ret;
> +}
> +
>  /*
>   * Software based L1D cache flush which is used when microcode providing
>   * the cache control MSR is not loaded.
> @@ -8097,6 +8132,9 @@ 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;

Or simply:

	kvm_has_bus_lock_exit = cpu_has_vmx_bus_lock_detection();


> +
>  	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 8bf97a81affd..779ea3b15134 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -105,7 +105,7 @@ 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 d39d6cf1d473..d96619ce7f66 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -134,6 +134,8 @@ 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;
> @@ -3578,6 +3580,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_SMALLER_MAXPHYADDR:
>  		r = (int) allow_smaller_maxphyaddr;
>  		break;
> +	case KVM_CAP_X86_BUS_LOCK_EXIT:

Hmm, it might make more sense to do:

		if (kvm_has_bus_lock_exit)
			r = KVM_BUS_LOCK_DETECTION_OFF |
			    KVM_BUS_LOCK_DETECTION_EXIT;
		else
			r = 0;

On the other hand I can see it being useful for userspace to know that
KVM itself supports bus lock detection, but hardware does not.
		
> +		r |= KVM_BUS_LOCK_DETECTION_OFF;
> +		if (kvm_has_bus_lock_exit)
> +			r |= KVM_BUS_LOCK_DETECTION_EXIT;
> +		break;
>  	default:
>  		break;
>  	}
> @@ -5030,6 +5037,20 @@ 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:
> +		r = -EINVAL;
> +		if (cap->args[0] & ~KVM_BUS_LOCK_DETECTION_VALID_MODE)
> +			break;
> +
> +		if ((cap->args[0] & KVM_BUS_LOCK_DETECTION_OFF) &&
> +		    (cap->args[0] & KVM_BUS_LOCK_DETECTION_EXIT))
> +			break;
> +
> +		if (kvm_has_bus_lock_exit &&
> +		    cap->args[0] & KVM_BUS_LOCK_DETECTION_EXIT)
> +			kvm->arch.bus_lock_exit = true;
> +		r = 0;
> +		break;
>  	default:
>  		r = -EINVAL;
>  		break;
> @@ -7772,12 +7793,16 @@ 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;
>  }
>  
>  static void update_cr8_intercept(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 995ab696dcf0..54aa7712cb52 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -335,6 +335,11 @@ 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)

I don't see any point in adding an accessor for a bool.

> +{
> +	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 f6d86033c4fa..3f0176733622 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. */
> @@ -1035,6 +1036,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_LAST_CPU 184
>  #define KVM_CAP_SMALLER_MAXPHYADDR 185
>  #define KVM_CAP_S390_DIAG318 186
> +#define KVM_CAP_X86_BUS_LOCK_EXIT 187
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -1689,4 +1691,9 @@ struct kvm_hyperv_eventfd {
>  #define KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE    (1 << 0)
>  #define KVM_DIRTY_LOG_INITIALLY_SET            (1 << 1)
>  
> +#define KVM_BUS_LOCK_DETECTION_OFF             (1 << 0)
> +#define KVM_BUS_LOCK_DETECTION_EXIT            (1 << 1)
> +#define KVM_BUS_LOCK_DETECTION_VALID_MODE      (KVM_BUS_LOCK_DETECTION_OFF | \
> +						KVM_BUS_LOCK_DETECTION_EXIT)

I don't think we want to define KVM_BUS_LOCK_DETECTION_VALID_MODE in the
uapi header, that should be kernel only.

> +
>  #endif /* __LINUX_KVM_H */
> -- 
> 2.17.1
>