linux-kernel - Re: [PATCH next] KVM: VMX: add noinstr for is_td_vcpu and is

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Message-ID: <20250527110706.GA20019@noisy.programming.kicks-ass.net>
Date: Tue, 27 May 2025 13:07:06 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Edward Adam Davis <eadavis@...com>
Cc: seanjc@...gle.com, pbonzini@...hat.com, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	binbin.wu@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] KVM: VMX: add noinstr for is_td_vcpu and is_td

On Tue, May 27, 2025 at 11:45:16AM +0800, Edward Adam Davis wrote:
> is_td() and is_td_vcpu() run in no instrumentation, so they are need
> noinstr.
> 
> [1]
> vmlinux.o: error: objtool: vmx_handle_nmi+0x47:
>         call to is_td_vcpu.isra.0() leaves .noinstr.text section
> 
> Fixes: 7172c753c26a ("KVM: VMX: Move common fields of struct vcpu_{vmx,tdx} to a struct")
> Signed-off-by: Edward Adam Davis <eadavis@...com>
> ---
>  arch/x86/kvm/vmx/common.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/common.h b/arch/x86/kvm/vmx/common.h
> index 8f46a06e2c44..70e0879c58f6 100644
> --- a/arch/x86/kvm/vmx/common.h
> +++ b/arch/x86/kvm/vmx/common.h
> @@ -59,20 +59,20 @@ struct vcpu_vt {
>  
>  #ifdef CONFIG_KVM_INTEL_TDX
>  
> -static __always_inline bool is_td(struct kvm *kvm)
> +static noinstr __always_inline bool is_td(struct kvm *kvm)

noinstr and __always_inline are not compatible. Specifically noinstr
implies noinline.

>  {
>  	return kvm->arch.vm_type == KVM_X86_TDX_VM;
>  }
>  
> -static __always_inline bool is_td_vcpu(struct kvm_vcpu *vcpu)
> +static noinstr __always_inline bool is_td_vcpu(struct kvm_vcpu *vcpu)
>  {
>  	return is_td(vcpu->kvm);
>  }
>  
>  #else
>  
> -static inline bool is_td(struct kvm *kvm) { return false; }
> -static inline bool is_td_vcpu(struct kvm_vcpu *vcpu) { return false; }
> +static noinstr bool is_td(struct kvm *kvm) { return false; }
> +static noinstr bool is_td_vcpu(struct kvm_vcpu *vcpu) { return false; }

The problem is likely your compiler is silly and managed to out-of-line
these; make these __always_inline and try again.

>  
>  #endif
>  
> -- 
> 2.43.0
>