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

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Message-ID: <ZAAsIBUuIIO1prZT@google.com>
Date:   Thu, 2 Mar 2023 04:54:56 +0000
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 02, 2023, Wang, Wei W wrote:
> On Thursday, March 2, 2023 3:47 AM, David Matlack wrote:
> > On Wed, Mar 1, 2023 at 5:38 AM Wei Wang <wei.w.wang@...el.com> wrote:
> > >
> > > Current KVM_BUG and KVM_BUG_ON assumes that 'cond' passed from
> > callers
> > > is 32-bit as it casts 'cond' to the type of int. This will be wrong if 'cond'
> > > provided by a caller is 64-bit, e.g. an error code of
> > > 0xc0000d0300000000 will be converted to 0, which is not expected.
> > > Improves the implementation by using !!(cond) in KVM_BUG and
> > > KVM_BUG_ON. Compared to changing 'int' to 'int64_t', this has less LOCs.
> > 
> > Less LOC is nice to have, but please preserve the behavior that "cond"
> > is evaluated only once by KVM_BUG() and KVM_BUG_ON(). i.e.
> > KVM_BUG_ON(do_something(), kvm) should only result in a single call to
> > do_something().
> 
> Good point, thanks! Using 'typeof(cond)' looks like a better choice.

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);					\
 								\
 	if (WARN_ONCE(__ret && !(kvm)->vm_bugged, fmt))		\
 		kvm_vm_bugged(kvm);				\
@@ -857,7 +857,7 @@ static inline void kvm_vm_bugged(struct kvm *kvm)

 #define KVM_BUG_ON(cond, kvm)					\
 ({								\
-	int __ret = (cond);					\
+	int __ret = !!(cond);					\
 								\
 	if (WARN_ON_ONCE(__ret && !(kvm)->vm_bugged))		\
 		kvm_vm_bugged(kvm);				\