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

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Message-ID: <CALzav=eRYpnfg7bVQpVawAMraFdHu3OzqWr55Pg1SJC_Uh8t=Q@mail.gmail.com>
Date:   Wed, 1 Mar 2023 11:47:25 -0800
From:   David Matlack <dmatlack@...gle.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
Subject: Re: [PATCH v1] KVM: allow KVM_BUG/KVM_BUG_ON to handle 64-bit cond

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().

>
> 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));                                     \
>  })