Re: [PATCH v2] KVM: s390: Pass initialized arg even if unused

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Thu, 25 Aug 2022 21:25:40 +0200
Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote:

> This silences smatch warnings reported by kbuild bot:
> arch/s390/kvm/gaccess.c:859 guest_range_to_gpas() error: uninitialized symbol 'prot'.
> arch/s390/kvm/gaccess.c:1064 access_guest_with_key() error: uninitialized symbol 'prot'.
> 
> This is because it cannot tell that the value is not used in this case.
> The trans_exc* only examine prot if code is PGM_PROTECTION.
> Pass a dummy value for other codes.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
> v1 -> v2
>  * drop unlikely, WARN_ON_ONCE instead of WARN (thanks Heiko)
> 
>  arch/s390/kvm/gaccess.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index 082ec5f2c3a5..0243b6e38d36 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -489,6 +489,8 @@ enum prot_type {
>  	PROT_TYPE_ALC  = 2,
>  	PROT_TYPE_DAT  = 3,
>  	PROT_TYPE_IEP  = 4,
> +	/* Dummy value for passing an initialized value when code != PGM_PROTECTION */
> +	PROT_NONE,
>  };
>  
>  static int trans_exc_ending(struct kvm_vcpu *vcpu, int code, unsigned long gva, u8 ar,
> @@ -504,6 +506,10 @@ static int trans_exc_ending(struct kvm_vcpu *vcpu, int code, unsigned long gva,
>  	switch (code) {
>  	case PGM_PROTECTION:
>  		switch (prot) {
> +		case PROT_NONE:
> +			/* We should never get here, acts like termination */
> +			WARN_ON_ONCE(1);
> +			break;
>  		case PROT_TYPE_IEP:
>  			tec->b61 = 1;
>  			fallthrough;
> @@ -968,8 +974,10 @@ static int guest_range_to_gpas(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>  				return rc;
>  		} else {
>  			gpa = kvm_s390_real_to_abs(vcpu, ga);
> -			if (kvm_is_error_gpa(vcpu->kvm, gpa))
> +			if (kvm_is_error_gpa(vcpu->kvm, gpa)) {
>  				rc = PGM_ADDRESSING;
> +				prot = PROT_NONE;
> +			}
>  		}
>  		if (rc)
>  			return trans_exc(vcpu, rc, ga, ar, mode, prot);
> @@ -1112,8 +1120,6 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>  		if (rc == PGM_PROTECTION && try_storage_prot_override)
>  			rc = access_guest_page_with_key(vcpu->kvm, mode, gpas[idx],
>  							data, fragment_len, PAGE_SPO_ACC);
> -		if (rc == PGM_PROTECTION)
> -			prot = PROT_TYPE_KEYC;
>  		if (rc)
>  			break;
>  		len -= fragment_len;
> @@ -1123,6 +1129,10 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>  	if (rc > 0) {
>  		bool terminate = (mode == GACC_STORE) && (idx > 0);
>  
> +		if (rc == PGM_PROTECTION)
> +			prot = PROT_TYPE_KEYC;
> +		else
> +			prot = PROT_NONE;
>  		rc = trans_exc_ending(vcpu, rc, ga, ar, mode, prot, terminate);
>  	}
>  out_unlock: