linux-kernel - Re: [PATCH 1/2] KVM: x86: introduce definitions to support static calls for kvm_x86

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Date:   Wed, 13 Jan 2021 13:53:39 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jason Baron <jbaron@...mai.com>, kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        peterz@...radead.org, aarcange@...hat.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: x86: introduce definitions to support static
 calls for kvm_x86_ops

On 11/01/21 17:57, Jason Baron wrote:
> +#define DEFINE_KVM_OPS_STATIC_CALL(func)	\
> +	DEFINE_STATIC_CALL_NULL(kvm_x86_##func,	\
> +				*(((struct kvm_x86_ops *)0)->func))
> +#define DEFINE_KVM_OPS_STATIC_CALLS() \
> +	FOREACH_KVM_X86_OPS(DEFINE_KVM_OPS_STATIC_CALL)

Something wrong here?

> +#define DECLARE_KVM_OPS_STATIC_CALL(func)	\
> +	DECLARE_STATIC_CALL(kvm_x86_##func,	\
> +			    *(((struct kvm_x86_ops *)0)->func))
> +#define DECLARE_KVM_OPS_STATIC_CALLS()		\
> +	FOREACH_KVM_X86_OPS(DECLARE_KVM_OPS_STATIC_CALL)
> +
> +#define KVM_OPS_STATIC_CALL_UPDATE(func)	\
> +	static_call_update(kvm_x86_##func, kvm_x86_ops.func)
> +#define KVM_OPS_STATIC_CALL_UPDATES()		\
> +	FOREACH_KVM_X86_OPS(KVM_OPS_STATIC_CALL_UPDATE)
> +
>   struct kvm_x86_ops {
>   	int (*hardware_enable)(void);
>   	void (*hardware_disable)(void);
> @@ -1326,6 +1385,12 @@ extern u64 __read_mostly host_efer;
>   extern bool __read_mostly allow_smaller_maxphyaddr;
>   extern struct kvm_x86_ops kvm_x86_ops;
>   
> +DECLARE_KVM_OPS_STATIC_CALLS();
> +static inline void kvm_ops_static_call_update(void)
> +{
> +	KVM_OPS_STATIC_CALL_UPDATES();
> +}

This would become

#define KVM_X86_OP(func) \
	DECLARE_STATIC_CALL(kvm_x86_##func,	\
			    *(((struct kvm_x86_ops *)0)->func));

#include <asm/kvm-x86-ops.h>

static inline void kvm_ops_static_call_update(void)
{
#define KVM_X86_OP(func) \
   static_call_update(kvm_x86_##func, kvm_x86_ops.func)
#include <asm/kvm-x86-ops.h>
}

If you need to choose between DECLARE_STATIC_CALL_NULL and 
DECLARE_STATIC_CALL, you can have kvm-x86-ops.h use one of two macros 
KVM_X86_OP_NULL and KVM_X86_OP.

#define KVM_X86_OP(func) \
	DECLARE_STATIC_CALL(kvm_x86_##func,	\
			    *(((struct kvm_x86_ops *)0)->func));

#define KVM_X86_OP_NULL(func) \
	DECLARE_STATIC_CALL_NULL(kvm_x86_##func,	\
			    *(((struct kvm_x86_ops *)0)->func));

#include <asm/kvm-x86-ops.h>

...

#define KVM_X86_OP(func) \
   static_call_update(kvm_x86_##func, kvm_x86_ops.func)
#define KVM_X86_OP_NULL(func) \
   static_call_update(kvm_x86_##func, kvm_x86_ops.func)
#include <asm/kvm-x86-ops.h>

In that case vmx.c and svm.c could define KVM_X86_OP_NULL to an empty 
string and list the optional callbacks manually.

Paolo