Subject: [PATCH v2 7/7] ARM: KVM: MMIO support BE host running LE code

From: [email-masked] (Christoffer Dall)
Date: Wed, 19 Mar 2014 18:12:30 -0700

On Tue, Feb 11, 2014 at 09:41:33PM -0800, Victor Kamensky wrote:
> In case of status register E bit is not set (LE mode) and host runs in
> BE mode we need byteswap data, so read/write is emulated correctly.
> 
> Signed-off-by: Victor Kamensky <[email-masked]>
> ---
>  arch/arm/include/asm/kvm_emulate.h | 22 ++++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
> index 0fa90c9..69b7469 100644
> --- a/arch/arm/include/asm/kvm_emulate.h
> +++ b/arch/arm/include/asm/kvm_emulate.h
> @@ -185,9 +185,16 @@ static inline unsigned long vcpu_data_guest_to_host(struct kvm_vcpu *vcpu,
>  		default:
>  			return be32_to_cpu(data);
>  		}
> +	} else {
> +		switch (len) {
> +		case 1:
> +			return data & 0xff;
> +		case 2:
> +			return le16_to_cpu(data & 0xffff);
> +		default:
> +			return le32_to_cpu(data);
> +		}
>  	}
> -
> -	return data;		/* Leave LE untouched */
>  }
>  
>  static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
> @@ -203,9 +210,16 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
>  		default:
>  			return cpu_to_be32(data);
>  		}
> +	} else {
> +		switch (len) {
> +		case 1:
> +			return data & 0xff;
> +		case 2:
> +			return cpu_to_le16(data & 0xffff);
> +		default:
> +			return cpu_to_le32(data);
> +		}
>  	}
> -
> -	return data;		/* Leave LE untouched */
>  }
>  
>  #endif /* __ARM_KVM_EMULATE_H__ */
> -- 
> 1.8.1.4
> 

Somehow in my head the way I think about this is

if (guest_be != host_be) {
	return swab(data);
}

but it's probably not more clear in terms of the actual code...

Anyway, given that the ABI clarification text gets merged:

Reviewed-by: Christoffer Dall <[email-masked]>