linux-kernel - Re: [PATCH v19 116/130] KVM: TDX: Silently discard SMI request

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Date: Fri, 19 Apr 2024 15:04:54 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: isaku.yamahata@...el.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com
Subject: Re: [PATCH v19 116/130] KVM: TDX: Silently discard SMI request



On 2/26/2024 4:26 PM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> TDX doesn't support system-management mode (SMM) and system-management
> interrupt (SMI) in guest TDs.  Because guest state (vcpu state, memory
> state) is protected, it must go through the TDX module APIs to change guest
> state, injecting SMI and changing vcpu mode into SMM.  The TDX module
> doesn't provide a way for VMM to inject SMI into guest TD and a way for VMM
                                                             ^
                                                             or

> to switch guest vcpu mode into SMM.
>
> We have two options in KVM when handling SMM or SMI in the guest TD or the
> device model (e.g. QEMU): 1) silently ignore the request or 2) return a
> meaningful error.
>
> For simplicity, we implemented the option 1).
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
[...]
> +
> +static void vt_enable_smi_window(struct kvm_vcpu *vcpu)
> +{
> +	if (is_td_vcpu(vcpu)) {
> +		tdx_enable_smi_window(vcpu);
> +		return;

Can "return tdx_enable_smi_window(vcpu);" directly.
> +	}
> +
> +	/* RSM will cause a vmexit anyway.  */
> +	vmx_enable_smi_window(vcpu);
> +}
> +#endif
> +
[...]
>   
> +#if defined(CONFIG_INTEL_TDX_HOST) && defined(CONFIG_KVM_SMM)
> +int tdx_smi_allowed(struct kvm_vcpu *vcpu, bool for_injection);
> +int tdx_enter_smm(struct kvm_vcpu *vcpu, union kvm_smram *smram);
> +int tdx_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram);
> +void tdx_enable_smi_window(struct kvm_vcpu *vcpu);
> +#else

#elif defined(CONFIG_KVM_SMM)

These functions are only needed when CONFIG_KVM_SMM is defined.

> +static inline int tdx_smi_allowed(struct kvm_vcpu *vcpu, bool for_injection) { return false; }
> +static inline int tdx_enter_smm(struct kvm_vcpu *vcpu, union kvm_smram *smram) { return 0; }
> +static inline int tdx_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram) { return 0; }
> +static inline void tdx_enable_smi_window(struct kvm_vcpu *vcpu) {}
> +#endif
> +
>   #endif /* __KVM_X86_VMX_X86_OPS_H */