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

Huang, Kai
2023-05-23T00:24:32Z

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@google.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
>