Re: [PATCH v3 04/18] x86/reboot: KVM: Disable SVM during reboot via virt/KVM reboot callback

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

On Fri, 2023-05-12 at 16:50 -0700, Sean Christopherson wrote:
> Use the virt callback to disable SVM (and set GIF=1) during an emergency
> instead of blindly attempting to disable SVM.  Like the VMX case, if a
> hypervisor, i.e. KVM, isn't loaded/active, SVM can't be in use.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>

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

> ---
>  arch/x86/include/asm/virtext.h |  8 --------
>  arch/x86/kernel/reboot.c       |  3 ---
>  arch/x86/kvm/svm/svm.c         | 19 +++++++++++++++++--
>  3 files changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
> index 5bc29fab15da..aaed66249ccf 100644
> --- a/arch/x86/include/asm/virtext.h
> +++ b/arch/x86/include/asm/virtext.h
> @@ -133,12 +133,4 @@ static inline void cpu_svm_disable(void)
>  	}
>  }
>  
> -/** Makes sure SVM is disabled, if it is supported on the CPU
> - */
> -static inline void cpu_emergency_svm_disable(void)
> -{
> -	if (cpu_has_svm(NULL))
> -		cpu_svm_disable();
> -}
> -
>  #endif /* _ASM_X86_VIRTEX_H */
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 0cf2261c2dec..92b380e199a3 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -826,9 +826,6 @@ void cpu_emergency_disable_virtualization(void)
>  	if (callback)
>  		callback();
>  	rcu_read_unlock();
> -
> -	/* KVM_AMD doesn't yet utilize the common callback. */
> -	cpu_emergency_svm_disable();
>  }
>  
>  #if defined(CONFIG_SMP)
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index eb308c9994f9..0f0d04900bf2 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -38,6 +38,7 @@
>  #include <asm/spec-ctrl.h>
>  #include <asm/cpu_device_id.h>
>  #include <asm/traps.h>
> +#include <asm/reboot.h>
>  #include <asm/fpu/api.h>
>  
>  #include <asm/virtext.h>
> @@ -568,6 +569,11 @@ void __svm_write_tsc_multiplier(u64 multiplier)
>  	preempt_enable();
>  }
>  
> +static void svm_emergency_disable(void)
> +{
> +	cpu_svm_disable();
> +}
> +
>  static void svm_hardware_disable(void)
>  {
>  	/* Make sure we clean up behind us */
> @@ -5184,6 +5190,13 @@ static struct kvm_x86_init_ops svm_init_ops __initdata = {
>  	.pmu_ops = &amd_pmu_ops,
>  };
>  
> +static void __svm_exit(void)
> +{
> +	kvm_x86_vendor_exit();
> +
> +	cpu_emergency_unregister_virt_callback(svm_emergency_disable);
> +}
> +
>  static int __init svm_init(void)
>  {
>  	int r;
> @@ -5197,6 +5210,8 @@ static int __init svm_init(void)
>  	if (r)
>  		return r;
>  
> +	cpu_emergency_register_virt_callback(svm_emergency_disable);
> +
>  	/*
>  	 * Common KVM initialization _must_ come last, after this, /dev/kvm is
>  	 * exposed to userspace!
> @@ -5209,14 +5224,14 @@ static int __init svm_init(void)
>  	return 0;
>  
>  err_kvm_init:
> -	kvm_x86_vendor_exit();
> +	__svm_exit();
>  	return r;
>  }
>  
>  static void __exit svm_exit(void)
>  {
>  	kvm_exit();
> -	kvm_x86_vendor_exit();
> +	__svm_exit();
>  }
>  
>  module_init(svm_init)
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>