Re: [PATCH] KVM: Disable irq while unregistering user notifier

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On 22/10/2016 00:08, Ignacio Alvarado wrote:
> Function user_notifier_unregister should be called only once for each
> registered user notifier.
> 
> Function kvm_arch_hardware_disable can be executed from an IPI context
> which could cause a race condition with a VCPU returning to user mode
> and attempting to unregister the notifier.
> 
> Signed-off-by: Ignacio Alvarado <ikalvarado@xxxxxxxxxx>

Should drop_user_return_notifiers instead be moved to kvm_arch_exit?

Thanks,

Paolo

> ---
>  arch/x86/kvm/x86.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e375235..51f87f0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -210,7 +210,15 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
>  	struct kvm_shared_msrs *locals
>  		= container_of(urn, struct kvm_shared_msrs, urn);
>  	struct kvm_shared_msr_values *values;
> +	unsigned long flags;
>  
> +	/*
> +	 * Disabling irqs at this point since the following code could be
> +	 * interrupted and executed through kvm_arch_hardware_disable()
> +	 */
> +	local_irq_save(flags);
> +	if (!locals->registered)
> +		goto out;
>  	for (slot = 0; slot < shared_msrs_global.nr; ++slot) {
>  		values = &locals->values[slot];
>  		if (values->host != values->curr) {
> @@ -220,6 +228,8 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
>  	}
>  	locals->registered = false;
>  	user_return_notifier_unregister(urn);
> +out:
> +	local_irq_restore(flags);
>  }
>  
>  static void shared_msr_update(unsigned slot, u32 msr)
> 
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