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Date: Thu, 3 Jun 2021 09:23:58 +0800
From: Tao Xu <tao3.xu@...el.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Xiaoyao Li <xiaoyao.li@...el.com>, pbonzini@...hat.com,
seanjc@...gle.com, wanpengli@...cent.com, jmattson@...gle.com,
joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
bp@...en8.de, hpa@...or.com
Subject: Re: [PATCH v2] KVM: VMX: Enable Notify VM exit
On 6/2/21 6:31 PM, Vitaly Kuznetsov wrote:
> Tao Xu <tao3.xu@...el.com> writes:
>
>> There are some cases that malicious virtual machines can cause CPU stuck
>> (event windows don't open up), e.g., infinite loop in microcode when
>> nested #AC (CVE-2015-5307). No event window obviously means no events,
>> e.g. NMIs, SMIs, and IRQs will all be blocked, may cause the related
>> hardware CPU can't be used by host or other VM.
>>
>> To resolve those cases, it can enable a notify VM exit if no event
>> window occur in VMX non-root mode for a specified amount of time
>> (notify window). Since CPU is first observed the risk of not causing
>> forward progress, after notify window time in a units of crystal clock,
>> Notify VM exit will happen. Notify VM exit can happen incident to delivery
>> of a vectored event.
>>
>> Expose a module param for configuring notify window, which is in unit of
>> crystal clock cycle.
>> - A negative value (e.g. -1) is to disable this feature.
>> - Make the default as 0. It is safe because an internal threshold is added
>> to notify window to ensure all the normal instructions being coverd.
>> - User can set it to a large value when they want to give more cycles to
>> wait for some reasons, e.g., silicon wrongly kill some normal instruction
>> due to internal threshold is too small.
>>
>> Notify VM exit is defined in latest Intel Architecture Instruction Set
>> Extensions Programming Reference, chapter 9.2.
>>
>> Co-developed-by: Xiaoyao Li <xiaoyao.li@...el.com>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
>> Signed-off-by: Tao Xu <tao3.xu@...el.com>
>> ---
>>
>> Changelog:
>> v2:
>> Default set notify window to 0, less than 0 to disable.
>> Add more description in commit message.
>
> Sorry if this was already discussed, but in case of nested
> virtualization and when L1 also enables
> SECONDARY_EXEC_NOTIFY_VM_EXITING, shouldn't we just reflect NOTIFY exits
> during L2 execution to L1 instead of crashing the whole L1?
>
Notify VM Exit will not crash L1 guest if VM context valid in exit
qualification. After VM exit, VMM can resume the guest normally.
>> ---
>> arch/x86/include/asm/vmx.h | 7 +++++
>> arch/x86/include/asm/vmxfeatures.h | 1 +
>> arch/x86/include/uapi/asm/vmx.h | 4 ++-
>> arch/x86/kvm/vmx/capabilities.h | 6 +++++
>> arch/x86/kvm/vmx/vmx.c | 42 ++++++++++++++++++++++++++++--
>> include/uapi/linux/kvm.h | 2 ++
>> 6 files changed, 59 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
>> index 0ffaa3156a4e..9104c85a973f 100644
>> --- a/arch/x86/include/asm/vmx.h
>> +++ b/arch/x86/include/asm/vmx.h
>> @@ -74,6 +74,7 @@
>> #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 SECONDARY_EXEC_NOTIFY_VM_EXITING VMCS_CONTROL_BIT(NOTIFY_VM_EXITING)
>>
>> #define PIN_BASED_EXT_INTR_MASK VMCS_CONTROL_BIT(INTR_EXITING)
>> #define PIN_BASED_NMI_EXITING VMCS_CONTROL_BIT(NMI_EXITING)
>> @@ -269,6 +270,7 @@ enum vmcs_field {
>> SECONDARY_VM_EXEC_CONTROL = 0x0000401e,
>> PLE_GAP = 0x00004020,
>> PLE_WINDOW = 0x00004022,
>> + NOTIFY_WINDOW = 0x00004024,
>> VM_INSTRUCTION_ERROR = 0x00004400,
>> VM_EXIT_REASON = 0x00004402,
>> VM_EXIT_INTR_INFO = 0x00004404,
>> @@ -555,6 +557,11 @@ enum vm_entry_failure_code {
>> #define EPT_VIOLATION_EXECUTABLE (1 << EPT_VIOLATION_EXECUTABLE_BIT)
>> #define EPT_VIOLATION_GVA_TRANSLATED (1 << EPT_VIOLATION_GVA_TRANSLATED_BIT)
>>
>> +/*
>> + * Exit Qualifications for NOTIFY VM EXIT
>> + */
>> +#define NOTIFY_VM_CONTEXT_INVALID BIT(0)
>> +
>> /*
>> * VM-instruction error numbers
>> */
>> diff --git a/arch/x86/include/asm/vmxfeatures.h b/arch/x86/include/asm/vmxfeatures.h
>> index d9a74681a77d..15f0f2ab4f95 100644
>> --- a/arch/x86/include/asm/vmxfeatures.h
>> +++ b/arch/x86/include/asm/vmxfeatures.h
>> @@ -84,5 +84,6 @@
>> #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 */
>> +#define VMX_FEATURE_NOTIFY_VM_EXITING ( 2*32+ 31) /* VM-Exit when no event windows after notify window */
>>
>> #endif /* _ASM_X86_VMXFEATURES_H */
>> diff --git a/arch/x86/include/uapi/asm/vmx.h b/arch/x86/include/uapi/asm/vmx.h
>> index 946d761adbd3..ef4c80f6553e 100644
>> --- a/arch/x86/include/uapi/asm/vmx.h
>> +++ b/arch/x86/include/uapi/asm/vmx.h
>> @@ -91,6 +91,7 @@
>> #define EXIT_REASON_UMWAIT 67
>> #define EXIT_REASON_TPAUSE 68
>> #define EXIT_REASON_BUS_LOCK 74
>> +#define EXIT_REASON_NOTIFY 75
>>
>> #define VMX_EXIT_REASONS \
>> { EXIT_REASON_EXCEPTION_NMI, "EXCEPTION_NMI" }, \
>> @@ -153,7 +154,8 @@
>> { EXIT_REASON_XRSTORS, "XRSTORS" }, \
>> { EXIT_REASON_UMWAIT, "UMWAIT" }, \
>> { EXIT_REASON_TPAUSE, "TPAUSE" }, \
>> - { EXIT_REASON_BUS_LOCK, "BUS_LOCK" }
>> + { EXIT_REASON_BUS_LOCK, "BUS_LOCK" }, \
>> + { EXIT_REASON_NOTIFY, "NOTIFY"}
>>
>> #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 8dee8a5fbc17..8527f34a84ac 100644
>> --- a/arch/x86/kvm/vmx/capabilities.h
>> +++ b/arch/x86/kvm/vmx/capabilities.h
>> @@ -407,4 +407,10 @@ static inline u64 vmx_supported_debugctl(void)
>> return debugctl;
>> }
>>
>> +static inline bool cpu_has_notify_vm_exiting(void)
>> +{
>> + return vmcs_config.cpu_based_2nd_exec_ctrl &
>> + SECONDARY_EXEC_NOTIFY_VM_EXITING;
>> +}
>> +
>> #endif /* __KVM_X86_VMX_CAPS_H */
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index 4bceb5ca3a89..c0ad01c88dac 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -205,6 +205,10 @@ module_param(ple_window_max, uint, 0444);
>> int __read_mostly pt_mode = PT_MODE_SYSTEM;
>> module_param(pt_mode, int, S_IRUGO);
>>
>> +/* Default is 0, less than 0 (for example, -1) disables notify window. */
>> +static int __read_mostly notify_window;
>> +module_param(notify_window, int, 0644);
>> +
>> static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
>> static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond);
>> static DEFINE_MUTEX(vmx_l1d_flush_mutex);
>> @@ -2539,7 +2543,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>> SECONDARY_EXEC_PT_USE_GPA |
>> SECONDARY_EXEC_PT_CONCEAL_VMX |
>> SECONDARY_EXEC_ENABLE_VMFUNC |
>> - SECONDARY_EXEC_BUS_LOCK_DETECTION;
>> + SECONDARY_EXEC_BUS_LOCK_DETECTION |
>> + SECONDARY_EXEC_NOTIFY_VM_EXITING;
>> if (cpu_has_sgx())
>> opt2 |= SECONDARY_EXEC_ENCLS_EXITING;
>> if (adjust_vmx_controls(min2, opt2,
>> @@ -4376,6 +4381,9 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
>> if (!vcpu->kvm->arch.bus_lock_detection_enabled)
>> exec_control &= ~SECONDARY_EXEC_BUS_LOCK_DETECTION;
>>
>> + if (cpu_has_notify_vm_exiting() && notify_window < 0)
>> + exec_control &= ~SECONDARY_EXEC_NOTIFY_VM_EXITING;
>> +
>> vmx->secondary_exec_control = exec_control;
>> }
>>
>> @@ -4423,6 +4431,9 @@ static void init_vmcs(struct vcpu_vmx *vmx)
>> vmx->ple_window_dirty = true;
>> }
>>
>> + if (cpu_has_notify_vm_exiting() && notify_window >= 0)
>> + vmcs_write32(NOTIFY_WINDOW, notify_window);
>> +
>> vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, 0);
>> vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, 0);
>> vmcs_write32(CR3_TARGET_COUNT, 0); /* 22.2.1 */
>> @@ -5642,6 +5653,31 @@ static int handle_bus_lock_vmexit(struct kvm_vcpu *vcpu)
>> return 0;
>> }
>>
>> +static int handle_notify(struct kvm_vcpu *vcpu)
>> +{
>> + unsigned long exit_qual = vmx_get_exit_qual(vcpu);
>> +
>> + if (!(exit_qual & NOTIFY_VM_CONTEXT_INVALID)) {
>> + /*
>> + * Notify VM exit happened while executing iret from NMI,
>> + * "blocked by NMI" bit has to be set before next VM entry.
>> + */
>> + if (enable_vnmi &&
>> + (exit_qual & INTR_INFO_UNBLOCK_NMI))
>> + vmcs_set_bits(GUEST_INTERRUPTIBILITY_INFO,
>> + GUEST_INTR_STATE_NMI);
>> +
>> + return 1;
>> + }
>> +
>> + vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
>> + vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_NO_EVENT_WINDOW;
>> + vcpu->run->internal.ndata = 1;
>> + vcpu->run->internal.data[0] = exit_qual;
>> +
>> + 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
>> @@ -5699,6 +5735,7 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
>> [EXIT_REASON_PREEMPTION_TIMER] = handle_preemption_timer,
>> [EXIT_REASON_ENCLS] = handle_encls,
>> [EXIT_REASON_BUS_LOCK] = handle_bus_lock_vmexit,
>> + [EXIT_REASON_NOTIFY] = handle_notify,
>> };
>>
>> static const int kvm_vmx_max_exit_handlers =
>> @@ -6042,7 +6079,8 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>> exit_reason.basic != EXIT_REASON_EPT_VIOLATION &&
>> exit_reason.basic != EXIT_REASON_PML_FULL &&
>> exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
>> - exit_reason.basic != EXIT_REASON_TASK_SWITCH)) {
>> + exit_reason.basic != EXIT_REASON_TASK_SWITCH &&
>> + exit_reason.basic != EXIT_REASON_NOTIFY)) {
>> int ndata = 3;
>>
>> vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 3fd9a7e9d90c..bb3b49b1fb0d 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -278,6 +278,8 @@ struct kvm_xen_exit {
>> #define KVM_INTERNAL_ERROR_DELIVERY_EV 3
>> /* Encounter unexpected vm-exit reason */
>> #define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON 4
>> +/* Encounter notify vm-exit */
>> +#define KVM_INTERNAL_ERROR_NO_EVENT_WINDOW 5
>>
>> /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
>> struct kvm_run {
>
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