linux-kernel - Re: [PATCH 2/3] x86: add guest_late_init hook to hypervisor

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Message-ID: <20171108091323.kidsiiim2mqenphf@gmail.com>
Date:   Wed, 8 Nov 2017 10:13:23 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        xen-devel@...ts.xenproject.org, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, boris.ostrovsky@...cle.com,
        pbonzini@...hat.com, rkrcmar@...hat.com, rjw@...ysocki.net,
        len.brown@...el.com, pavel@....cz
Subject: Re: [PATCH 2/3] x86: add guest_late_init hook to hypervisor_x86
 structure


* Juergen Gross <jgross@...e.com> wrote:

> Add a new guest_late_init hook to the hypervisor_x86 structure. It
> will replace the current kvm_guest_init() call which is changed to
> make use of the new hook.
> 
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  arch/x86/include/asm/hypervisor.h | 11 +++++++++++
>  arch/x86/include/asm/kvm_para.h   |  2 --
>  arch/x86/kernel/kvm.c             |  3 ++-
>  arch/x86/kernel/setup.c           |  2 +-
>  4 files changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/hypervisor.h b/arch/x86/include/asm/hypervisor.h
> index 0ead9dbb9130..37320687b8cb 100644
> --- a/arch/x86/include/asm/hypervisor.h
> +++ b/arch/x86/include/asm/hypervisor.h
> @@ -38,6 +38,9 @@ struct hypervisor_x86 {
>  	/* Platform setup (run once per boot) */
>  	void		(*init_platform)(void);
>  
> +	/* Guest late init */
> +	void		(*guest_late_init)(void);
> +
>  	/* X2APIC detection (run once per boot) */
>  	bool		(*x2apic_available)(void);
>  
> @@ -66,9 +69,17 @@ static inline void hypervisor_init_mem_mapping(void)
>  	if (x86_hyper && x86_hyper->init_mem_mapping)
>  		x86_hyper->init_mem_mapping();
>  }
> +
> +static inline void hypervisor_guest_late_init(void)
> +{
> +	if (x86_hyper && x86_hyper->guest_late_init)
> +		x86_hyper->guest_late_init();
> +}
> +
>  #else
>  static inline void init_hypervisor_platform(void) { }
>  static inline bool hypervisor_x2apic_available(void) { return false; }
>  static inline void hypervisor_init_mem_mapping(void) { }
> +static inline void hypervisor_guest_late_init(void) { }
>  #endif /* CONFIG_HYPERVISOR_GUEST */
>  #endif /* _ASM_X86_HYPERVISOR_H */
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index c373e44049b1..7b407dda2bd7 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -88,7 +88,6 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1,
>  #ifdef CONFIG_KVM_GUEST
>  bool kvm_para_available(void);
>  unsigned int kvm_arch_para_features(void);
> -void __init kvm_guest_init(void);
>  void kvm_async_pf_task_wait(u32 token, int interrupt_kernel);
>  void kvm_async_pf_task_wake(u32 token);
>  u32 kvm_read_and_reset_pf_reason(void);
> @@ -103,7 +102,6 @@ static inline void kvm_spinlock_init(void)
>  #endif /* CONFIG_PARAVIRT_SPINLOCKS */
>  
>  #else /* CONFIG_KVM_GUEST */
> -#define kvm_guest_init() do {} while (0)
>  #define kvm_async_pf_task_wait(T, I) do {} while(0)
>  #define kvm_async_pf_task_wake(T) do {} while(0)
>  
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 8bb9594d0761..d331b5060aa9 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -465,7 +465,7 @@ static void __init kvm_apf_trap_init(void)
>  	update_intr_gate(X86_TRAP_PF, async_page_fault);
>  }
>  
> -void __init kvm_guest_init(void)
> +static void __init kvm_guest_init(void)
>  {
>  	int i;
>  
> @@ -548,6 +548,7 @@ const struct hypervisor_x86 x86_hyper_kvm __refconst = {
>  	.name			= "KVM",
>  	.detect			= kvm_detect,
>  	.x2apic_available	= kvm_para_available,
> +	.guest_late_init	= kvm_guest_init,
>  };
>  EXPORT_SYMBOL_GPL(x86_hyper_kvm);
>  
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 0957dd73d127..578569481d87 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1294,7 +1294,7 @@ void __init setup_arch(char **cmdline_p)
>  
>  	io_apic_init_mappings();
>  
> -	kvm_guest_init();
> +	hypervisor_guest_late_init();

No principal objections, but could we please use a more obvious pattern showing 
that this is a callback, by calling it directly:
	
	x86_hyper->guest_late_init();

Plus add a default empty function (which hypervisors can override). This avoids 
all the hidden conditions and wrappery.

Thanks,

	Ingo