linux-kernel - Re: [PATCH v1] KVM: allow KVM_BUG/KVM_BUG

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Date:   Thu, 2 Mar 2023 10:12:17 -0800
From:   Mingwei Zhang <mizhang@...gle.com>
To:     "Wang, Wei W" <wei.w.wang@...el.com>
Cc:     David Matlack <dmatlack@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] KVM: allow KVM_BUG/KVM_BUG_ON to handle 64-bit cond

On Thu, Mar 2, 2023 at 2:26 AM Wang, Wei W <wei.w.wang@...el.com> wrote:
>
> On Thursday, March 2, 2023 12:55 PM, Mingwei Zhang wrote:
> > I don't get it. Why bothering the type if we just do this?
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index
> > 4f26b244f6d0..10455253c6ea 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -848,7 +848,7 @@ static inline void kvm_vm_bugged(struct kvm *kvm)
> >
> >  #define KVM_BUG(cond, kvm, fmt...)                           \
> >  ({                                                           \
> > -     int __ret = (cond);                                     \
> > +     int __ret = !!(cond);                                   \
>
> This is essentially "bool __ret". No biggie to change it this way.

!! will return an int, not a boolean, but it is used as a boolean.
This is consistent with the original code which _is_ returning an
integer.

> But I'm inclined to retain the original intention to have the macro return
> the value that was passed in:
> typeof(cond) __ret = (cond);

hmm, I think it is appropriate to retain the original type of 'cond'
especially since it may also involve other arithmetic operations. But
I doubt it will be very useful. For instance, who is going to write
this code?

......
if (KVM_BUG(cond, true) & some_mask)
  do_something()
......

>
> Let's what others vote for.

Please fix this bug first before introducing nice features.

Thanks.
-Mingwei


-Mingwei