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

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

[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>
---
 arch/s390/kvm/gaccess.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 082ec5f2c3a5..89186701116a 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,
@@ -503,6 +505,7 @@ static int trans_exc_ending(struct kvm_vcpu *vcpu, int code, unsigned long gva,
 
 	switch (code) {
 	case PGM_PROTECTION:
+		WARN(unlikely(prot == PROT_NONE), "Invalid prot argument");
 		switch (prot) {
 		case PROT_TYPE_IEP:
 			tec->b61 = 1;
@@ -519,6 +522,8 @@ static int trans_exc_ending(struct kvm_vcpu *vcpu, int code, unsigned long gva,
 		case PROT_TYPE_DAT:
 			tec->b61 = 1;
 			break;
+		case PROT_NONE:
+			/* We should never get here, acts like termination */
 		}
 		if (terminate) {
 			tec->b56 = 0;
@@ -968,8 +973,10 @@ 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 +1119,6 @@ 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 +1128,10 @@ 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:
-- 
2.34.1

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

[Heiko Carstens]

On Wed, Aug 24, 2022 at 05:30:11PM +0200, Janis Schoetterl-Glausch 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>
> ---
>  arch/s390/kvm/gaccess.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
...
> @@ -503,6 +505,7 @@ static int trans_exc_ending(struct kvm_vcpu *vcpu, int code, unsigned long gva,
>  
>  	switch (code) {
>  	case PGM_PROTECTION:
> +		WARN(unlikely(prot == PROT_NONE), "Invalid prot argument");

The WARN macro comes with unlikely, please get rid of unlikely here. Also:

> +		case PROT_NONE:
> +			/* We should never get here, acts like termination */

Why not put it here? And make it WARN_ON_ONCE() in addition?

>  			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 == PGM_PROTECTION)
> +			prot = PROT_TYPE_KEYC;
> +		else
> +			prot = PROT_NONE;

For both cases I would suggest to preinitialize prot with PROT_NONE in
order to keep the code smaller - but not my call.

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

[Janis Schoetterl-Glausch]

On Thu, 2022-08-25 at 10:30 +0200, Heiko Carstens wrote:
> On Wed, Aug 24, 2022 at 05:30:11PM +0200, Janis Schoetterl-Glausch 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>
> > ---
> >  arch/s390/kvm/gaccess.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)

[...]

> >  			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 == PGM_PROTECTION)
> > +			prot = PROT_TYPE_KEYC;
> > +		else
> > +			prot = PROT_NONE;
> 
> For both cases I would suggest to preinitialize prot with PROT_NONE in
> order to keep the code smaller - but not my call.

I chose this to make it really obvious that PROT_NONE is used only in
cases where code != PGM_PROTECTION.