linux-kernel - Re: [PATCH v5 01/22] KVM: arm64: Introduce template for inline functions

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Date:   Wed, 23 Mar 2022 20:16:10 +0800
From:   Gavin Shan <gshan@...hat.com>
To:     Oliver Upton <oupton@...gle.com>
Cc:     kvmarm@...ts.cs.columbia.edu, maz@...nel.org,
        linux-kernel@...r.kernel.org, eauger@...hat.com,
        shan.gavin@...il.com, Jonathan.Cameron@...wei.com,
        pbonzini@...hat.com, vkuznets@...hat.com, will@...nel.org
Subject: Re: [PATCH v5 01/22] KVM: arm64: Introduce template for inline
 functions

Hi Oliver,

On 3/23/22 3:42 AM, Oliver Upton wrote:
> On Tue, Mar 22, 2022 at 04:06:49PM +0800, Gavin Shan wrote:
>> The inline functions used to get the SMCCC parameters have same
>> layout. It means these functions can be presented by an unified
>> template, to make the code simplified. Besides, this adds more
>> similar inline functions like smccc_get_arg{4,5,6,7,8}() to get
>> more SMCCC arguments, which are needed by SDEI virtualization
>> support.
>>
>> Signed-off-by: Gavin Shan <gshan@...hat.com>
>> ---
>>   include/kvm/arm_hypercalls.h | 24 ++++++++++++------------
>>   1 file changed, 12 insertions(+), 12 deletions(-)
>>
>> diff --git a/include/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h
>> index 0e2509d27910..d5144c852fe4 100644
>> --- a/include/kvm/arm_hypercalls.h
>> +++ b/include/kvm/arm_hypercalls.h
>> @@ -13,20 +13,20 @@ static inline u32 smccc_get_function(struct kvm_vcpu *vcpu)
>>   	return vcpu_get_reg(vcpu, 0);
>>   }
>>   
>> -static inline unsigned long smccc_get_arg1(struct kvm_vcpu *vcpu)
>> -{
>> -	return vcpu_get_reg(vcpu, 1);
>> -}
>> -
>> -static inline unsigned long smccc_get_arg2(struct kvm_vcpu *vcpu)
>> -{
>> -	return vcpu_get_reg(vcpu, 2);
>> +#define SMCCC_DECLARE_GET_ARG(reg)					\
>> +static inline unsigned long smccc_get_arg##reg(struct kvm_vcpu *vcpu)	\
>> +{									\
>> +	return vcpu_get_reg(vcpu, reg);					\
>>   }
>>   
>> -static inline unsigned long smccc_get_arg3(struct kvm_vcpu *vcpu)
>> -{
>> -	return vcpu_get_reg(vcpu, 3);
>> -}
>> +SMCCC_DECLARE_GET_ARG(1)
>> +SMCCC_DECLARE_GET_ARG(2)
>> +SMCCC_DECLARE_GET_ARG(3)
>> +SMCCC_DECLARE_GET_ARG(4)
>> +SMCCC_DECLARE_GET_ARG(5)
>> +SMCCC_DECLARE_GET_ARG(6)
>> +SMCCC_DECLARE_GET_ARG(7)
>> +SMCCC_DECLARE_GET_ARG(8)
> 
> Hmm. What if we specify a single inline function where the caller passes
> the arg # as a parameter? We really just want to abstract away the
> off-by-one difference between GP registers and SMCCC arguments.
> 
> Macros generally make me uneasy for template functions, but I may be in
> the vocal minority on this topic :)
> 

I think it's a good idea to have smccc_get_arg(unsigned char index).
However, it will cause more code changes because the following functions
have been used. Anyway, I think it's still worthy to pass @index to
differentiate the argument index. I will change it accordingly in
next respin.

    smccc_get_arg1()
    smccc_get_arg2()
    smccc_get_arg3()

Thanks,
Gavin