Re: [PATCH v3 1/2] x86/kvm/vmx: Move IRQ/NMI dispatch from KVM into x86 core

[Nathan Chancellor]

On Tue, May 26, 2026 at 11:06:31AM +0200, Peter Zijlstra wrote:
> 
> Sorry, I missed this :/

No worries, I should have pinged about it elsewhere sooner.

> Subject: x86/kvm/vmx: Fix x86_64 CFI build
> 
> I missed that idt_do_interrupt_irqoff() gets compiled on x84_64; this is
> a problem for CFI builds because it includes an unadorned indirect call.
> It is however completely dead code.
> 
> Rework things to not emit this function at all.
> 
> Fixes: 0701c9e17bd9 ("x86/kvm/vmx: Move IRQ/NMI dispatch from KVM into x86 core")
> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Reported-by: Calvin Owens <calvin@xxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>

> ---
> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index 06c7c6ebd6f9..14cd43d4da6c 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -55,7 +55,7 @@ noinstr void x86_entry_from_kvm(unsigned int event_type, unsigned int vector)
>  	 * The FRED NMI context is significantly different and will not work
>  	 * right (specifically FRED fixed the NMI recursion issue).
>  	 */
> -	idt_entry_from_kvm(vector);
> +	idt_do_nmi_irqoff();
>  }
>  EXPORT_SYMBOL_FOR_KVM(x86_entry_from_kvm);
>  #endif
> diff --git a/arch/x86/entry/entry.S b/arch/x86/entry/entry.S
> index a56e043b266d..2bc217bb5475 100644
> --- a/arch/x86/entry/entry.S
> +++ b/arch/x86/entry/entry.S
> @@ -109,11 +109,13 @@ EXPORT_SYMBOL(__ref_stack_chk_guard);
>  	RET
>  .endm
>  
> +#ifndef CONFIG_X86_64
>  .pushsection .text, "ax"
>  SYM_FUNC_START(idt_do_interrupt_irqoff)
>  	IDT_DO_EVENT_IRQOFF CALL_NOSPEC _ASM_ARG1
>  SYM_FUNC_END(idt_do_interrupt_irqoff)
>  .popsection
> +#endif
>  
>  .pushsection .noinstr.text, "ax"
>  SYM_FUNC_START(idt_do_nmi_irqoff)
> diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
> index 7bcf1decc034..90a22e24a9eb 100644
> --- a/arch/x86/kernel/idt.c
> +++ b/arch/x86/kernel/idt.c
> @@ -268,18 +268,10 @@ void __init idt_setup_early_pf(void)
>  }
>  #endif
>  
> -#if IS_ENABLED(CONFIG_KVM_INTEL)
> -noinstr void idt_entry_from_kvm(unsigned int vector)
> +#if IS_ENABLED(CONFIG_KVM_INTEL) && !defined(CONFIG_X86_64)
> +void idt_entry_from_kvm(unsigned int vector)
>  {
> -	if (vector == NMI_VECTOR)
> -		return idt_do_nmi_irqoff();
> -
> -	/*
> -	 * Only the NMI path requires noinstr.
> -	 */
> -	instrumentation_begin();
>  	idt_do_interrupt_irqoff(gate_offset(idt_table + vector));
> -	instrumentation_end();
>  }
>  #endif
>  

-- 
Cheers,
Nathan