linux-kernel - Re: [PATCH] KVM: x86: Fix function address when kvm_x86

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Date:   Tue, 22 Feb 2022 16:54:54 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Fix function address when kvm_x86_ops.func is
 NULL

On 22/2/2022 4:33 pm, Paolo Bonzini wrote:
> On 2/22/22 07:25, Like Xu wrote:
>> From: Like Xu <likexu@...cent.com>
>>
>> Fix the function address for __static_call_return0() which is used by
>> static_call_update() when a func in struct kvm_x86_ops is NULL.
>>
>> Fixes: 5be2226f417d ("KVM: x86: allow defining return-0 static calls")
>> Signed-off-by: Like Xu <likexu@...cent.com>
> 
> Sorry for the stupid question, but what breaks?

Although they are numerically the same, I suppose we should use the
& operator here, as in the other cases where __static_call_return0 is used.

What's more, Clang complains about the KVM_X86_OP_OPTIONAL_RET0 change:

./arch/x86/include/asm/kvm-x86-ops.h:108:1: warning: pointer type mismatch \
	('bool (*)(struct kvm_vcpu *)' (aka '_Bool (*)(struct kvm_vcpu *)') and 'void *') \
	[-Wpointer-type-mismatch]
and more warnings from [-Wpointer-type-mismatch]

Does it help you ?

> 
> Paolo
> 
>> ---
>>   arch/x86/include/asm/kvm_host.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 713e08f62385..312f5ee19514 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -1548,7 +1548,7 @@ static inline void kvm_ops_static_call_update(void)
>>   #define KVM_X86_OP_OPTIONAL __KVM_X86_OP
>>   #define KVM_X86_OP_OPTIONAL_RET0(func) \
>>       static_call_update(kvm_x86_##func, kvm_x86_ops.func ? : \
>> -               (void *) __static_call_return0);
>> +               (void *)&__static_call_return0);
>>   #include <asm/kvm-x86-ops.h>
>>   #undef __KVM_X86_OP
>>   }
>