Subject: Re: [PATCH v3 2/9] KVM: x86: Move init-only kvm_x86_ops to separate struct

From: Sean Christopherson <[email-masked]>
Date: Mon, 23 Mar 2020 09:31:36 -0700

On Mon, Mar 23, 2020 at 05:24:56PM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <[email-masked]> writes:
> 
> > On Mon, Mar 23, 2020 at 01:10:40PM +0100, Vitaly Kuznetsov wrote:
> >> Sean Christopherson <[email-masked]> writes:
> >> 
> >> > +
> >> > +	.runtime_ops = &svm_x86_ops,
> >> > +};
> >> 
> >> Unrelated to your patch but I think we can make the naming of some of
> >> these functions more consistend on SVM/VMX, in particular I'd suggest 
> >> 
> >> has_svm() -> cpu_has_svm_support()
> >> is_disabled -> svm_disabled_by_bios()
> >> ...
> >> (see below for VMX)
> >> 
> >> > +
> >> >  static int __init svm_init(void)
> >> >  {
> >> > -	return kvm_init(&svm_x86_ops, sizeof(struct vcpu_svm),
> >> > +	return kvm_init(&svm_init_ops, sizeof(struct vcpu_svm),
> >> >  			__alignof__(struct vcpu_svm), THIS_MODULE);
> >> >  }
> >> >  
> >> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> >> > index 07299a957d4a..ffcdcc86f5b7 100644
> >> > --- a/arch/x86/kvm/vmx/vmx.c
> >> > +++ b/arch/x86/kvm/vmx/vmx.c
> >> > @@ -7842,11 +7842,8 @@ static bool vmx_check_apicv_inhibit_reasons(ulong bit)
> >> >  }
> >> >  
> >> >  static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
> >> > -	.cpu_has_kvm_support = cpu_has_kvm_support,
> >> > -	.disabled_by_bios = vmx_disabled_by_bios,
> >> > -	.hardware_setup = hardware_setup,
> >> >  	.hardware_unsetup = hardware_unsetup,
> >> > -	.check_processor_compatibility = vmx_check_processor_compat,
> >> > +
> >> >  	.hardware_enable = hardware_enable,
> >> >  	.hardware_disable = hardware_disable,
> >> >  	.cpu_has_accelerated_tpr = report_flexpriority,
> >> > @@ -7981,6 +7978,15 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
> >> >  	.apic_init_signal_blocked = vmx_apic_init_signal_blocked,
> >> >  };
> >> >  
> >> > +static struct kvm_x86_init_ops vmx_init_ops __initdata = {
> >> > +	.cpu_has_kvm_support = cpu_has_kvm_support,
> >> > +	.disabled_by_bios = vmx_disabled_by_bios,
> >> > +	.check_processor_compatibility = vmx_check_processor_compat,
> >> > +	.hardware_setup = hardware_setup,
> >> 
> >> cpu_has_kvm_support() -> cpu_has_vmx_support()
> >> hardware_setup() -> vmx_hardware_setup()
> >
> > Preaching to the choir on this one.  The VMX functions without prefixes in
> > in particular annoy me to no end, e.g. hardware_setup().  Though the worst
> > is probably ".vcpu_create = vmx_create_vcpu", if I had a nickel for every
> > time I've tried to find vmx_vcpu_create()...
> >
> > What if we added a macro to auto-generate the common/required hooks?  E.g.:
> >
> >   static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
> > 	MANDATORY_KVM_X86_OPS(vmx),
> >
> > 	.pmu_ops = &intel_pmu_ops,
> >
> > 	...
> >   };
> >
> > That'd enforce consistent naming, and would provide a bit of documentation
> > as to which hooks are optional, e.g. many of the nested hooks, and which
> > must be defined for KVM to function.
> 
> Sounds cool! (not sure that with only two implementations people won't
> call it 'over-engineered' but cool). My personal wish would just be that
> function names in function implementations are not auto-generated so
> e.g. a simple 'git grep vmx_hardware_setup' works but the way how we
> fill vmx_x86_ops in can be macroed I guess.

Ya, I was thinking of just the macro.  Even that has downsides though, e.g.
chasing kvm_x86_ops.hardware_setup() to find VMX's hardware_setup() becomes
a bit kludgy.  On the other hand, _if_ you know how the fill macro works,
getting to the implementation should be easier.

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