Re: [PATCH v3 08/18] x86/reboot: Expose VMCS crash hooks if and only if KVM_{INTEL,AMD} is enabled

["Huang, Kai" <kai.huang@intel.com>]

On Fri, 2023-05-12 at 16:50 -0700, Sean Christopherson wrote:
> Expose the crash/reboot hooks used by KVM to disable virtualization in
> hardware and unblock INIT only if there's a potential in-tree user,
> i.e. either KVM_INTEL or KVM_AMD is enabled.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Kai Huang <kai.huang@intel.com>

> ---
>  arch/x86/include/asm/reboot.h | 4 ++++
>  arch/x86/kernel/reboot.c      | 5 ++++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/reboot.h b/arch/x86/include/asm/reboot.h
> index d9a38d379d18..9cf0b21bf495 100644
> --- a/arch/x86/include/asm/reboot.h
> +++ b/arch/x86/include/asm/reboot.h
> @@ -25,10 +25,14 @@ void __noreturn machine_real_restart(unsigned int type);
>  #define MRR_BIOS	0
>  #define MRR_APM		1
>  
> +#if IS_ENABLED(CONFIG_KVM_INTEL) || IS_ENABLED(CONFIG_KVM_AMD)
>  typedef void (cpu_emergency_virt_cb)(void);
>  void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback);
>  void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback);
>  void cpu_emergency_disable_virtualization(void);
> +#else
> +static inline void cpu_emergency_disable_virtualization(void) {}
> +#endif /* CONFIG_KVM_INTEL || CONFIG_KVM_AMD */
>  
>  typedef void (*nmi_shootdown_cb)(int, struct pt_regs*);
>  void nmi_panic_self_stop(struct pt_regs *regs);
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 493d66e59a4f..6818d8de85a1 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -529,6 +529,7 @@ static inline void kb_wait(void)
>  
>  static inline void nmi_shootdown_cpus_on_restart(void);
>  
> +#if IS_ENABLED(CONFIG_KVM_INTEL) || IS_ENABLED(CONFIG_KVM_AMD)
>  /* RCU-protected callback to disable virtualization prior to reboot. */
>  static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback;
>  
> @@ -596,7 +597,9 @@ static void emergency_reboot_disable_virtualization(void)
>  		nmi_shootdown_cpus_on_restart();
>  	}
>  }
> -
> +#else
> +static void emergency_reboot_disable_virtualization(void) { }
> +#endif /* CONFIG_KVM_INTEL || CONFIG_KVM_AMD */
>  
>  void __attribute__((weak)) mach_reboot_fixups(void)
>  {
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>