linux-kernel - Re: [PATCH v3 16/16] objtool: Validate kCFI calls

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Message-ID: <93595fc9-4d18-4739-8e40-bd4d70b1c1ba@zytor.com>
Date: Fri, 25 Jul 2025 17:33:23 -0700
From: Xin Li <xin@...or.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, kys@...rosoft.com,
        haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, pbonzini@...hat.com,
        ardb@...nel.org, kees@...nel.org, Arnd Bergmann <arnd@...db.de>,
        gregkh@...uxfoundation.org, jpoimboe@...nel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-efi@...r.kernel.org,
        samitolvanen@...gle.com, ojeda@...nel.org
Subject: Re: [PATCH v3 16/16] objtool: Validate kCFI calls

On 7/25/2025 12:56 PM, Sean Christopherson wrote:
>>
>> BTW, there is a declaration for vmx_do_interrupt_irqoff() in
>> arch/x86/kvm/vmx/vmx.c, so we'd better also do:
>>
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -6945,7 +6945,9 @@ void vmx_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64
>> *eoi_exit_bitmap)
>>          vmcs_write64(EOI_EXIT_BITMAP3, eoi_exit_bitmap[3]);
>>   }
>>
>> +#ifndef CONFIG_X86_FRED
>>   void vmx_do_interrupt_irqoff(unsigned long entry);
>> +#endif
> No, we want to keep the declaration.  Unconditionally decaring the symbol allows
> KVM to use IS_ENABLED():
> 
> 	if (IS_ENABLED(CONFIG_X86_FRED))
>   		fred_entry_from_kvm(EVENT_TYPE_EXTINT, vector);
> 
> Hiding the declaration would require that to be a "proper" #ifdef, which would
> be a net negative for readability.  The extra declaration won't hurt anything for
> CONFIG_X86_FRED=n, as "bad" usage will still fail at link time.

I did hit a compilation error, so yes, we have to keep it.