linux-kernel - Re: [PATCH v3 6/6] KVM: x86: allow defining return-0 static calls

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Message-ID: <Yg/YaOgTLixP2K8s@google.com>
Date:   Fri, 18 Feb 2022 17:33:28 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 6/6] KVM: x86: allow defining return-0 static calls

On Fri, Feb 18, 2022, Paolo Bonzini wrote:
> On 2/18/22 17:29, Sean Christopherson wrote:
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index ab1c4778824a..d3da64106685 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -131,6 +131,7 @@ struct kvm_x86_ops kvm_x86_ops __read_mostly;
> > >   	DEFINE_STATIC_CALL_NULL(kvm_x86_##func,			     \
> > >   				*(((struct kvm_x86_ops *)0)->func));
> > >   #define KVM_X86_OP_OPTIONAL KVM_X86_OP
> > > +#define KVM_X86_OP_OPTIONAL_RET0 KVM_X86_OP
> > >   #include <asm/kvm-x86-ops.h>
> > >   EXPORT_STATIC_CALL_GPL(kvm_x86_get_cs_db_l_bits);
> > >   EXPORT_STATIC_CALL_GPL(kvm_x86_cache_reg);
> > > @@ -12016,7 +12017,6 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
> > >   static inline bool kvm_guest_apic_has_interrupt(struct kvm_vcpu *vcpu)
> > >   {
> > >   	return (is_guest_mode(vcpu) &&
> > > -			kvm_x86_ops.guest_apic_has_interrupt &&
> > >   			static_call(kvm_x86_guest_apic_has_interrupt)(vcpu));
> > 
> > Can you opportunistically align the indentation and drop the outer parantheses? I.e.
> > 
> > 	return is_guest_mode(vcpu) &&
> > 	       static_call(kvm_x86_guest_apic_has_interrupt)(vcpu);
> 
> Hmm, I like having the parentheses (despite "return not being a function")
> because editors are inconsistent in what indentation to use after return.
> 
> Some use a tab (which does the right thing just by chance with Linux because
> "return " is as long as a tab is wide), but vim for example does the totally

Uh, no, vim inserts a tab.  "return " isn't as long as a tab is wide.  That's 7
chars, tabs are 8, which is exactly the problem.

I'm ok with
	
	return (is_guest_mode(vcpu) &&
		static_call(kvm_x86_guest_apic_has_interrupt)(vcpu));

I care more about alignment than unnecessary (), but I'd still prefer

	return is_guest_mode(vcpu) &&
	       static_call(kvm_x86_guest_apic_has_interrupt)(vcpu));

> awkward
> 
> int f()
> {
>         return a &&
>                 b;
> }
> 
> Of course I can fix the indentation.
> 
> Paolo
> 
> > >   }
> > > diff --git a/kernel/static_call.c b/kernel/static_call.c
> > > index 43ba0b1e0edb..76abd46fe6ee 100644
> > > --- a/kernel/static_call.c
> > > +++ b/kernel/static_call.c
> > > @@ -503,6 +503,7 @@ long __static_call_return0(void)
> > >   {
> > >   	return 0;
> > >   }
> > > +EXPORT_SYMBOL_GPL(__static_call_return0)
> > 
> > This doesn't compile, it needs a semicolon.
> > 
>