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 13:10:34 +0100
From:   Michael Mueller <mimu@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        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 24.02.22 12:36, Claudio Imbrenda wrote:
> 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


we do that at several places

arch/s390/kernel/processor.c:	for_each_set_bit_inv(bit, (long 
*)&stfle_fac_list, MAX_FACILITY_BIT)
arch/s390/kvm/interrupt.c:	set_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned 
long *) gisa);
arch/s390/kvm/kvm-s390.c:		set_bit_inv(vcpu->vcpu_id, (unsigned long *) 
sca->mcn);
arch/s390/kvm/kvm-s390.c:		set_bit_inv(vcpu->vcpu_id, (unsigned long *) 
&sca->mcn);

> 
>>   }
>>   
>>   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)
>