linux-kernel - Re: [PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr

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Date:   Mon, 26 Feb 2018 14:46:22 -0800
From:   Guenter Roeck <groeck@...gle.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel <linux-kernel@...r.kernel.org>,
        Guenter Roeck <groeck@...omium.org>
Subject: Re: [PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

On Mon, Feb 26, 2018 at 2:42 PM, Matthias Kaehlcke <mka@...omium.org> wrote:
> The type 'enum kvm_reg_ex' is an extension of 'enum kvm_reg', however
> the extension is only semantical and the compiler doesn't know about the
> relationship between the two types. In kvm_pdptr_read() a value of the
> extended type is passed to kvm_x86_ops->cache_reg(), which expects a
> value of the base type. Clang raises the following warning about the
> type mismatch:
>
> arch/x86/kvm/kvm_cache_regs.h:44:32: warning: implicit conversion from
>   enumeration type 'enum kvm_reg_ex' to different enumeration type
>   'enum kvm_reg' [-Wenum-conversion]
>     kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);
>
> Cast VCPU_EXREG_PDPTR to 'enum kvm_reg' to make the compiler happy.
>
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>

Reviewed-by: Guenter Roeck <groeck@...omium.org>

> ---
>  arch/x86/kvm/kvm_cache_regs.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
> index f500293dad8d..58ba12071014 100644
> --- a/arch/x86/kvm/kvm_cache_regs.h
> +++ b/arch/x86/kvm/kvm_cache_regs.h
> @@ -41,7 +41,7 @@ static inline u64 kvm_pdptr_read(struct kvm_vcpu *vcpu, int index)
>
>         if (!test_bit(VCPU_EXREG_PDPTR,
>                       (unsigned long *)&vcpu->arch.regs_avail))
> -               kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);
> +               kvm_x86_ops->cache_reg(vcpu, (enum kvm_reg)VCPU_EXREG_PDPTR);
>
>         return vcpu->arch.walk_mmu->pdptrs[index];
>  }
> --
> 2.16.1.291.g4437f3f132-goog
>