linux-kernel - Re: [PATCH v19 118/130] KVM: TDX: Add methods to ignore accesses to CPU state

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Date: Fri, 19 Apr 2024 18:04:10 +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 118/130] KVM: TDX: Add methods to ignore accesses to
 CPU state



On 2/26/2024 4:27 PM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> TDX protects TDX guest state from VMM.  Implement access methods for TDX
> guest state to ignore them or return zero.  Because those methods can be
> called by kvm ioctls to set/get cpu registers, they don't have KVM_BUG_ON
> except one method.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>   arch/x86/kvm/vmx/main.c    | 289 +++++++++++++++++++++++++++++++++----
>   arch/x86/kvm/vmx/tdx.c     |  48 +++++-
>   arch/x86/kvm/vmx/x86_ops.h |  13 ++
>   3 files changed, 321 insertions(+), 29 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 84d2dc818cf7..9fb3f28d8259 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -375,6 +375,200 @@ static void vt_vcpu_deliver_init(struct kvm_vcpu *vcpu)
>   	kvm_vcpu_deliver_init(vcpu);
>   }
>   
> +static void vt_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> +{
> +	if (is_td_vcpu(vcpu))
> +		return;
> +
> +	vmx_vcpu_after_set_cpuid(vcpu);
> +}
> +
> +static void vt_update_exception_bitmap(struct kvm_vcpu *vcpu)
> +{
> +	if (is_td_vcpu(vcpu))
> +		return;
> +
> +	vmx_update_exception_bitmap(vcpu);
> +}
> +
> +static u64 vt_get_segment_base(struct kvm_vcpu *vcpu, int seg)
> +{
> +	if (is_td_vcpu(vcpu))
> +		return tdx_get_segment_base(vcpu, seg);
Could just return 0?
Not need to add a function, since it's only called here and it's more 
straight forward to read the code without jump to the definition of 
these functions.

Similarly, we can use open code for tdx_get_cpl(), tdx_get_rflags() and 
tdx_get_segment(), which return 0 or memset with 0.


> +
> +	return vmx_get_segment_base(vcpu, seg);
> +}
> +
[...]
>   
> +int tdx_get_cpl(struct kvm_vcpu *vcpu)
> +{
> +	return 0;
> +}
> +
[...]
> +
> +unsigned long tdx_get_rflags(struct kvm_vcpu *vcpu)
> +{
> +	return 0;
> +}
> +
> +u64 tdx_get_segment_base(struct kvm_vcpu *vcpu, int seg)
> +{
> +	return 0;
> +}
> +
> +void tdx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
> +{
> +	memset(var, 0, sizeof(*var));
> +}
> +
>   static int tdx_get_capabilities(struct kvm_tdx_cmd *cmd)
>   {
>   	struct kvm_tdx_capabilities __user *user_caps;
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index 7c63b2b48125..727c4d418601 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -169,6 +169,12 @@ bool tdx_has_emulated_msr(u32 index, bool write);
>   int tdx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr);
>   int tdx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr);
>   
> +int tdx_get_cpl(struct kvm_vcpu *vcpu);
> +void tdx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg);
> +unsigned long tdx_get_rflags(struct kvm_vcpu *vcpu);
> +u64 tdx_get_segment_base(struct kvm_vcpu *vcpu, int seg);
> +void tdx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
> +
>   int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
>   
>   void tdx_flush_tlb(struct kvm_vcpu *vcpu);
> @@ -221,6 +227,13 @@ static inline bool tdx_has_emulated_msr(u32 index, bool write) { return false; }
>   static inline int tdx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) { return 1; }
>   static inline int tdx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) { return 1; }
>   
> +static inline int tdx_get_cpl(struct kvm_vcpu *vcpu) { return 0; }
> +static inline void tdx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg) {}
> +static inline unsigned long tdx_get_rflags(struct kvm_vcpu *vcpu) { return 0; }
> +static inline u64 tdx_get_segment_base(struct kvm_vcpu *vcpu, int seg) { return 0; }
> +static inline void tdx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var,
> +				   int seg) {}
> +
>   static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }
>   
>   static inline void tdx_flush_tlb(struct kvm_vcpu *vcpu) {}