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

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Message-ID: <YwczITkxvvghyvWq@osiris>
Date:   Thu, 25 Aug 2022 10:30:25 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
Cc:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        kernel test robot <lkp@...el.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        Sven Schnelle <svens@...ux.ibm.com>, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: s390: Pass initialized arg even if unused

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@...el.com>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.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.