linux-kernel - Re: [PATCH v1 1/1] KVM: s390: Don't cast parameter in bit operations

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Date:   Thu, 24 Feb 2022 12:36:20 +0100
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v1 1/1] KVM: s390: Don't cast parameter in bit
 operations

On Wed, 23 Feb 2022 18:44:20 +0200
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> While in this particular case it would not be a (critical) issue,
> the pattern itself is bad and error prone in case somebody blindly
> copies to their code.
> 
> Don't cast parameter to unsigned long pointer in the bit operations.
> Instead copy to a local variable on stack of a proper type and use.
> 
> Fixes: d77e64141e32 ("KVM: s390: implement GISA IPM related primitives")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  arch/s390/include/asm/kvm_host.h | 5 ++++-
>  arch/s390/kvm/interrupt.c        | 6 +++---
>  2 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index a22c9266ea05..f1c4a1b9b360 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -867,7 +867,10 @@ struct kvm_s390_gisa {
>  			u8  reserved03[11];
>  			u32 airq_count;
>  		} g1;
> -		struct {
> +		struct { /* as a 256-bit bitmap */
> +			DECLARE_BITMAP(b, 256);
> +		} bitmap;
> +		struct { /* as a set of 64-bit words */
>  			u64 word[4];
>  		} u64;
>  	};
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index db933c252dbc..04e055cbd080 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -304,7 +304,7 @@ static inline int gisa_in_alert_list(struct kvm_s390_gisa *gisa)
>  
>  static inline void gisa_set_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
>  {
> -	set_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
> +	set_bit_inv(IPM_BIT_OFFSET + gisc, gisa->bitmap.b);

wouldn't it be enough to pass gisa->u64.word here?
then no cast would be necessary

>  }
>  
>  static inline u8 gisa_get_ipm(struct kvm_s390_gisa *gisa)
> @@ -314,12 +314,12 @@ static inline u8 gisa_get_ipm(struct kvm_s390_gisa *gisa)
>  
>  static inline void gisa_clear_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
>  {
> -	clear_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
> +	clear_bit_inv(IPM_BIT_OFFSET + gisc, gisa->bitmap.b);
>  }
>  
>  static inline int gisa_tac_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
>  {
> -	return test_and_clear_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
> +	return test_and_clear_bit_inv(IPM_BIT_OFFSET + gisc, gisa->bitmap.b);
>  }
>  
>  static inline unsigned long pending_irqs_no_gisa(struct kvm_vcpu *vcpu)