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

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Date:   Wed, 1 Mar 2023 17:17:19 -0800
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     pbonzini@...hat.com, seanjc@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com
Subject: Re: [PATCH v1] KVM: allow KVM_BUG/KVM_BUG_ON to handle 64-bit cond

On Wed, Mar 01, 2023 at 09:38:41PM +0800,
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.

This changes its semantics. cond is evaluated twice. Also the return value
of KVM_BUG_ON() is changed to bool. typeof?
Perhaps return type of bool is okay, though.

Thanks,


> Fixes: 0b8f11737cff ("KVM: Add infrastructure and macro to mark VM as bugged")
> Signed-off-by: Wei Wang <wei.w.wang@...el.com>
> ---
>  include/linux/kvm_host.h | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f06635b24bd0..d77ddf82c5c8 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -881,20 +881,16 @@ static inline void kvm_vm_bugged(struct kvm *kvm)
>  
>  #define KVM_BUG(cond, kvm, fmt...)				\
>  ({								\
> -	int __ret = (cond);					\
> -								\
> -	if (WARN_ONCE(__ret && !(kvm)->vm_bugged, fmt))		\
> +	if (WARN_ONCE(!!cond && !(kvm)->vm_bugged, fmt))	\
>  		kvm_vm_bugged(kvm);				\
> -	unlikely(__ret);					\
> +	unlikely(!!cond);					\
>  })
>  
>  #define KVM_BUG_ON(cond, kvm)					\
>  ({								\
> -	int __ret = (cond);					\
> -								\
> -	if (WARN_ON_ONCE(__ret && !(kvm)->vm_bugged))		\
> +	if (WARN_ON_ONCE(!!(cond) && !(kvm)->vm_bugged))	\
>  		kvm_vm_bugged(kvm);				\
> -	unlikely(__ret);					\
> +	unlikely(!!(cond));					\
>  })
>  
>  static inline void kvm_vcpu_srcu_read_lock(struct kvm_vcpu *vcpu)
> -- 
> 2.27.0
> 

-- 
Isaku Yamahata <isaku.yamahata@...il.com>