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

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Date:   Wed, 8 Nov 2017 10:27:10 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Ingo Molnar <mingo@...nel.org>
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

On 08/11/17 10:13, Ingo Molnar wrote:
> 
> * 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.

Hmm, x86_hyper is just a pointer being NULL on bare metal. So we would
have to add a pre-filled struct with dummy functions and in case a
hypervisor is detected we'd need to copy all non-NULL pointers of the
hypervisor specific struct to the pre-filled one.

In case there are no objections I can add a patch to modify the current
way x86_hyper is used to the pre-filled variant.


Juergen