[PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

[PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

[Matthias Kaehlcke]

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@chromium.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

Re: [PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

[Guenter Roeck]

On Mon, Feb 26, 2018 at 2:42 PM, Matthias Kaehlcke <mka@chromium.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@chromium.org>

Reviewed-by: Guenter Roeck <groeck@chromium.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
>

Re: [PATCH] KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

[Radim Krčmář]

2018-02-26 14:42-0800, Matthias Kaehlcke:
> 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:

Yeah, expressing this in C type system seems impossible.

> 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@chromium.org>
> ---

Applied, thanks.