linux-kernel - Re: [PATCH] kvm: x86: vmx: avoid returning bool to distinguish success from error

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Message-ID: <545980A9.8030405@intel.com>
Date:	Wed, 05 Nov 2014 09:43:05 +0800
From:	"Chen, Tiejun" <tiejun.chen@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH] kvm: x86: vmx: avoid returning bool to distinguish success
 from error

On 2014/11/5 1:33, Paolo Bonzini wrote:
> Return a negative error code instead, and WARN() when we should be covering
> the entire 2-bit space of vmcs_field_type's return value.  For increased
> robustness, add a BUILD_BUG_ON checking the range of vmcs_field_to_offset.
>
> Suggested-by: Tiejun Chen <tiejun.chen@...el.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>   arch/x86/kvm/vmx.c | 51 +++++++++++++++++++++++++++++++--------------------
>   1 file changed, 31 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 12f6f9a8dd8d..0ee148f1687f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -720,12 +720,15 @@ static const unsigned short vmcs_field_to_offset_table[] = {
>   	FIELD(HOST_RSP, host_rsp),
>   	FIELD(HOST_RIP, host_rip),
>   };
> -static const int max_vmcs_field = ARRAY_SIZE(vmcs_field_to_offset_table);
>
>   static inline short vmcs_field_to_offset(unsigned long field)
>   {
> -	if (field >= max_vmcs_field || vmcs_field_to_offset_table[field] == 0)
> -		return -1;
> +	BUILD_BUG_ON(ARRAY_SIZE(vmcs_field_to_offset_table) > SHRT_MAX);
> +
> +	if (field >= ARRAY_SIZE(vmcs_field_to_offset_table) ||
> +	    vmcs_field_to_offset_table[field] == 0)
> +		return -ENOENT;
> +
>   	return vmcs_field_to_offset_table[field];
>   }
>
> @@ -6492,58 +6495,60 @@ static inline int vmcs_field_readonly(unsigned long field)
>    * some of the bits we return here (e.g., on 32-bit guests, only 32 bits of
>    * 64-bit fields are to be returned).
>    */
> -static inline bool vmcs12_read_any(struct kvm_vcpu *vcpu,
> -					unsigned long field, u64 *ret)
> +static inline int vmcs12_read_any(struct kvm_vcpu *vcpu,
> +				  unsigned long field, u64 *ret)
>   {
>   	short offset = vmcs_field_to_offset(field);
>   	char *p;
>
>   	if (offset < 0)
> -		return 0;
> +		return offset;
>
>   	p = ((char *)(get_vmcs12(vcpu))) + offset;
>
>   	switch (vmcs_field_type(field)) {
>   	case VMCS_FIELD_TYPE_NATURAL_WIDTH:
>   		*ret = *((natural_width *)p);
> -		return 1;
> +		return 0;
>   	case VMCS_FIELD_TYPE_U16:
>   		*ret = *((u16 *)p);
> -		return 1;
> +		return 0;
>   	case VMCS_FIELD_TYPE_U32:
>   		*ret = *((u32 *)p);
> -		return 1;
> +		return 0;
>   	case VMCS_FIELD_TYPE_U64:
>   		*ret = *((u64 *)p);
> -		return 1;
> +		return 0;
>   	default:
> -		return 0; /* can never happen. */
> +		WARN_ON(1);
> +		return -ENOENT;
>   	}
>   }
>
>
> -static inline bool vmcs12_write_any(struct kvm_vcpu *vcpu,
> -				    unsigned long field, u64 field_value){
> +static inline int vmcs12_write_any(struct kvm_vcpu *vcpu,
> +				   unsigned long field, u64 field_value){
>   	short offset = vmcs_field_to_offset(field);
>   	char *p = ((char *) get_vmcs12(vcpu)) + offset;
>   	if (offset < 0)
> -		return false;
> +		return offset;
>
>   	switch (vmcs_field_type(field)) {
>   	case VMCS_FIELD_TYPE_U16:
>   		*(u16 *)p = field_value;
> -		return true;
> +		return 0;
>   	case VMCS_FIELD_TYPE_U32:
>   		*(u32 *)p = field_value;
> -		return true;
> +		return 0;
>   	case VMCS_FIELD_TYPE_U64:
>   		*(u64 *)p = field_value;
> -		return true;
> +		return 0;
>   	case VMCS_FIELD_TYPE_NATURAL_WIDTH:
>   		*(natural_width *)p = field_value;
> -		return true;
> +		return 0;
>   	default:
> -		return false; /* can never happen. */
> +		WARN_ON(1);
> +		return -ENOENT;
>   	}
>
>   }
> @@ -6576,6 +6581,9 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx)
>   		case VMCS_FIELD_TYPE_NATURAL_WIDTH:
>   			field_value = vmcs_readl(field);
>   			break;
> +		default:
> +			WARN_ON(1);
> +			continue;

'continue' versus 'break'?

Thanks
Tiejun

>   		}
>   		vmcs12_write_any(&vmx->vcpu, field, field_value);
>   	}
> @@ -6621,6 +6629,9 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx)
>   			case VMCS_FIELD_TYPE_NATURAL_WIDTH:
>   				vmcs_writel(field, (long)field_value);
>   				break;
> +			default:
> +				WARN_ON(1);
> +				break;
>   			}
>   		}
>   	}
> @@ -6659,7 +6670,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
>   	/* Decode instruction info and find the field to read */
>   	field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
>   	/* Read the field, zero-extended to a u64 field_value */
> -	if (!vmcs12_read_any(vcpu, field, &field_value)) {
> +	if (vmcs12_read_any(vcpu, field, &field_value) < 0) {
>   		nested_vmx_failValid(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT);
>   		skip_emulated_instruction(vcpu);
>   		return 1;
>
--
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