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

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 25.08.22 um 21:25 schrieb Janis Schoetterl-Glausch:
> 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>

Thanks applied.
> ---
> 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: