linux-kernel - Re: [PATCH v3 17/18] KVM: x86: Force kvm_rebooting=true during emergency reboot/crash

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Date:   Mon, 22 May 2023 23:25:21 +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 17/18] KVM: x86: Force kvm_rebooting=true during
 emergency reboot/crash

On Fri, 2023-05-12 at 16:50 -0700, Sean Christopherson wrote:
> Set kvm_rebooting when virtualization is disabled in an emergency so that
> KVM eats faults on virtualization instructions even if kvm_reboot() isn't
> reached.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/svm.c | 2 ++
>  arch/x86/kvm/vmx/vmx.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 2cc195d95d32..d00da133b14f 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -611,6 +611,8 @@ static inline void kvm_cpu_svm_disable(void)
>  
>  static void svm_emergency_disable(void)
>  {
> +	kvm_rebooting = true;
> +
>  	kvm_cpu_svm_disable();
>  }
>  
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 008914396180..1dec932aff21 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -771,6 +771,8 @@ static void vmx_emergency_disable(void)
>  	int cpu = raw_smp_processor_id();
>  	struct loaded_vmcs *v;
>  
> +	kvm_rebooting = true;

Do we need a memory barrier here?

> +
>  	list_for_each_entry(v, &per_cpu(loaded_vmcss_on_cpu, cpu),
>  			    loaded_vmcss_on_cpu_link)
>  		vmcs_clear(v->vmcs);
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>