Re: [PATCH v2] xen/events: remove event handling recursion detection

[Boris Ostrovsky]

On 11/28/19 3:45 AM, Juergen Gross wrote:
> -
>  static void __xen_evtchn_do_upcall(void)
>  {
>  	struct vcpu_info *vcpu_info = __this_cpu_read(xen_vcpu);
> -	int cpu = get_cpu();
> -	unsigned count;
> +	int cpu = smp_processor_id();
>  
>  	do {
>  		vcpu_info->evtchn_upcall_pending = 0;
>  
> -		if (__this_cpu_inc_return(xed_nesting_count) - 1)
> -			goto out;
> -
>  		xen_evtchn_handle_events(cpu);
>  
>  		BUG_ON(!irqs_disabled());
>  
> -		count = __this_cpu_read(xed_nesting_count);
> -		__this_cpu_write(xed_nesting_count, 0);
> -	} while (count != 1 || vcpu_info->evtchn_upcall_pending);
> -
> -out:
> +		rmb(); /* Hypervisor can set upcall pending. */

virt_rmb() perhaps then?

-boris

>  
> -	put_cpu();
> +	} while (vcpu_info->evtchn_upcall_pending);
>  }
>  
>  void xen_evtchn_do_upcall(struct pt_regs *regs)