linux-kernel - Re: [PATCH v5 11/30] KVM: Add arch hook for reboot event

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Message-ID: <Y0cn0nnDV/8SrWQn@google.com>
Date:   Wed, 12 Oct 2022 20:47:14 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     isaku.yamahata@...el.com
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        isaku.yamahata@...il.com, Kai Huang <kai.huang@...el.com>,
        Chao Gao <chao.gao@...el.com>,
        Atish Patra <atishp@...shpatra.org>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Huang Ying <ying.huang@...el.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v5 11/30] KVM: Add arch hook for reboot event

On Thu, Sep 22, 2022, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Factor out the logic on reboot event as arch hook.  Later kvm/x86 overrides
> it.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---

...

> @@ -5135,6 +5141,8 @@ static void kvm_del_vm(void)
>  static int kvm_reboot(struct notifier_block *notifier, unsigned long val,
>  		      void *v)
>  {
> +	int r;
> +
>  	/*
>  	 * Some (well, at least mine) BIOSes hang on reboot if
>  	 * in vmx root mode.
> @@ -5143,8 +5151,14 @@ static int kvm_reboot(struct notifier_block *notifier, unsigned long val,
>  	 */
>  	pr_info("kvm: exiting hardware virtualization\n");
>  	kvm_rebooting = true;
> -	on_each_cpu(hardware_disable_nolock, NULL, 1);
> -	return NOTIFY_OK;
> +
> +	/* This hook is called without cpuhotplug disabled.  */
> +	cpus_read_lock();
> +	mutex_lock(&kvm_lock);
> +	r = kvm_arch_reboot(val);

Unless there's a valid use case for rejecting/stopping reboot, which I'm pretty
sure there isn't, don't allow arch code to return a value.  I.e. return NOTIFY_OK
unconditionally from kvm_reboot() and drop the return from kvm_arch_reboot().

> +	mutex_unlock(&kvm_lock);
> +	cpus_read_unlock();
> +	return r;
>  }
>  
>  static struct notifier_block kvm_reboot_notifier = {
> -- 
> 2.25.1
>