linux-kernel - Re: [PATCH v3 07/18] x86/reboot: Hoist "disable virt" helpers above "emergency reboot" path

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Message-ID: <26f9525ca5ade60e352f280ac4723354b45ac1a2.camel@intel.com>
Date:   Mon, 22 May 2023 13:11:16 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Gao, Chao" <chao.gao@...el.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v3 07/18] x86/reboot: Hoist "disable virt" helpers above
 "emergency reboot" path

On Fri, 2023-05-12 at 16:50 -0700, Sean Christopherson wrote:
> Move the various "disable virtualization" helpers above the emergency
> reboot path so that emergency_reboot_disable_virtualization() can be
> stubbed out in a future patch if neither KVM_INTEL nor KVM_AMD is enabled,
> i.e. if there is no in-tree user of CPU virtualization.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Personally I think this patch can be merged to next one.  Doing so may also
result in a more readable patch but I am not sure.

Anyway,

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

> ---
>  arch/x86/kernel/reboot.c | 90 ++++++++++++++++++++--------------------
>  1 file changed, 45 insertions(+), 45 deletions(-)
> 
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index fddfea5f1d20..493d66e59a4f 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -529,6 +529,51 @@ static inline void kb_wait(void)
>  
>  static inline void nmi_shootdown_cpus_on_restart(void);
>  
> +/* RCU-protected callback to disable virtualization prior to reboot. */
> +static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback;
> +
> +void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback)
> +{
> +	if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback)))
> +		return;
> +
> +	rcu_assign_pointer(cpu_emergency_virt_callback, callback);
> +}
> +EXPORT_SYMBOL_GPL(cpu_emergency_register_virt_callback);
> +
> +void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback)
> +{
> +	if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback) != callback))
> +		return;
> +
> +	rcu_assign_pointer(cpu_emergency_virt_callback, NULL);
> +	synchronize_rcu();
> +}
> +EXPORT_SYMBOL_GPL(cpu_emergency_unregister_virt_callback);
> +
> +/*
> + * Disable virtualization, i.e. VMX or SVM, to ensure INIT is recognized during
> + * reboot.  VMX blocks INIT if the CPU is post-VMXON, and SVM blocks INIT if
> + * GIF=0, i.e. if the crash occurred between CLGI and STGI.
> + */
> +void cpu_emergency_disable_virtualization(void)
> +{
> +	cpu_emergency_virt_cb *callback;
> +
> +	/*
> +	 * IRQs must be disabled as KVM enables virtualization in hardware via
> +	 * function call IPIs, i.e. IRQs need to be disabled to guarantee
> +	 * virtualization stays disabled.
> +	 */
> +	lockdep_assert_irqs_disabled();
> +
> +	rcu_read_lock();
> +	callback = rcu_dereference(cpu_emergency_virt_callback);
> +	if (callback)
> +		callback();
> +	rcu_read_unlock();
> +}
> +
>  static void emergency_reboot_disable_virtualization(void)
>  {
>  	local_irq_disable();
> @@ -785,54 +830,9 @@ void machine_crash_shutdown(struct pt_regs *regs)
>  }
>  #endif
>  
> -/* RCU-protected callback to disable virtualization prior to reboot. */
> -static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback;
> -
> -void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback)
> -{
> -	if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback)))
> -		return;
> -
> -	rcu_assign_pointer(cpu_emergency_virt_callback, callback);
> -}
> -EXPORT_SYMBOL_GPL(cpu_emergency_register_virt_callback);
> -
> -void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback)
> -{
> -	if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback) != callback))
> -		return;
> -
> -	rcu_assign_pointer(cpu_emergency_virt_callback, NULL);
> -	synchronize_rcu();
> -}
> -EXPORT_SYMBOL_GPL(cpu_emergency_unregister_virt_callback);
> -
>  /* This is the CPU performing the emergency shutdown work. */
>  int crashing_cpu = -1;
>  
> -/*
> - * Disable virtualization, i.e. VMX or SVM, to ensure INIT is recognized during
> - * reboot.  VMX blocks INIT if the CPU is post-VMXON, and SVM blocks INIT if
> - * GIF=0, i.e. if the crash occurred between CLGI and STGI.
> - */
> -void cpu_emergency_disable_virtualization(void)
> -{
> -	cpu_emergency_virt_cb *callback;
> -
> -	/*
> -	 * IRQs must be disabled as KVM enables virtualization in hardware via
> -	 * function call IPIs, i.e. IRQs need to be disabled to guarantee
> -	 * virtualization stays disabled.
> -	 */
> -	lockdep_assert_irqs_disabled();
> -
> -	rcu_read_lock();
> -	callback = rcu_dereference(cpu_emergency_virt_callback);
> -	if (callback)
> -		callback();
> -	rcu_read_unlock();
> -}
> -
>  #if defined(CONFIG_SMP)
>  
>  static nmi_shootdown_cb shootdown_callback;
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>