[PATCH] KVM: x86: Fix function address when kvm_x86_ops.func is NULL

[PATCH] KVM: x86: Fix function address when kvm_x86_ops.func is NULL

[Like Xu]

From: Like Xu <likexu@tencent.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@tencent.com>
---
 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
 }
-- 
2.35.0

Re: [PATCH] KVM: x86: Fix function address when kvm_x86_ops.func is NULL

[Paolo Bonzini]

On 2/22/22 07:25, Like Xu wrote:
> From: Like Xu <likexu@tencent.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@tencent.com>

Sorry for the stupid question, but what breaks?

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
>   }

Re: [PATCH] KVM: x86: Fix function address when kvm_x86_ops.func is NULL

[Like Xu]

On 22/2/2022 4:33 pm, Paolo Bonzini wrote:
> On 2/22/22 07:25, Like Xu wrote:
>> From: Like Xu <likexu@tencent.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@tencent.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
>>   }
> 

Re: [PATCH] KVM: x86: Fix function address when kvm_x86_ops.func is NULL

[Sean Christopherson]

On Tue, Feb 22, 2022, Like Xu wrote:
> On 22/2/2022 4:33 pm, Paolo Bonzini wrote:
> > On 2/22/22 07:25, Like Xu wrote:
> > > From: Like Xu <likexu@tencent.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@tencent.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.

Meh, IMO all the other instances are weird for adding the "&".