Re: [PATCH] arch/x86/entry_fred: don't set up KVM IRQs if KVM is disabled

[Thomas Gleixner]

On Fri, Feb 16 2024 at 07:31, Paolo Bonzini wrote:
> On 2/16/24 03:10, Xin Li wrote:
>
> It is intentional that KVM-related things are compiled out completely
> if !IS_ENABLED(CONFIG_KVM), because then it's also not necessary to
> have

That's a matter of taste. In both cases _ALL_ KVM related things are
compiled out.

#ifdeffing out the vector numbers is silly to begin with because these
vector numbers stay assigned to KVM whether KVM is enabled or not.

And no, I don't think it's a net win to have the #ifdeffery in that
table. Look at apic_idts[] in arch/x86/kernel/idt.c how this ends up
looking. It's unreadable gunk.

The few NULL defines in a header file next to the real stuff

#if IS_ENABLED(CONFIG_KVM)
....
#else
# define fred_sysvec_kvm_posted_intr_ipi                NULL
# define fred_sysvec_kvm_posted_intr_wakeup_ipi         NULL
# define fred_sysvec_kvm_posted_intr_nested_ipi         NULL
#endif

are not hurting at all and they are at a place where #ifdeffery is
required anyway. That's a very common pattern all over the kernel and it
limits the #ifdef horror to _ONE_ place.

With your change you propagate the #ifdefffery to the multiple and the
very wrong places for absolutely zero practical value. The resulting
binary code is exactly the same for the price of tasteless #ifdeffery in
places where it matters.

Please get rid of this #ifdef in the vector header and don't inflict
bad taste on everyone.

Thanks,

        tglx