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Message-ID: <871r9k36ds.fsf@vitty.brq.redhat.com>
Date: Wed, 02 Jun 2021 12:31:11 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Tao Xu <tao3.xu@...el.com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Tao Xu <tao3.xu@...el.com>, 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
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?
> ---
> 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 {
--
Vitaly
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