linux-kernel - Re: [PATCH v2 2/3] xen/events: Return -EEXIST for bound VIRQs

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Message-ID: <2d7bceff-d70f-4f17-b833-380ffc06577e@suse.com>
Date: Wed, 27 Aug 2025 17:21:19 +0200
From: Jürgen Groß <jgross@...e.com>
To: Jason Andryuk <jason.andryuk@....com>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] xen/events: Return -EEXIST for bound VIRQs

On 26.08.25 02:55, Jason Andryuk wrote:
> Change find_virq() to return -EEXIST when a VIRQ is bound to a
> different CPU than the one passed in.  With that, remove the BUG_ON()
> from bind_virq_to_irq() to propogate the error upwards.
> 
> Some VIRQs are per-cpu, but others are per-domain or global.  Those must
> be bound to CPU0 and can then migrate elsewhere.  The lookup for
> per-domain and global will probably fail when migrated off CPU 0,
> especially when the current CPU is tracked.  This now returns -EEXIST
> instead of BUG_ON().
> 
> A second call to bind a per-domain or global VIRQ is not expected, but
> make it non-fatal to avoid trying to look up the irq, since we don't
> know which per_cpu(virq_to_irq) it will be in.
> 
> Signed-off-by: Jason Andryuk <jason.andryuk@....com>
> ---
> V2:
> New
> ---
>   drivers/xen/events/events_base.c | 17 ++++++++++++-----
>   1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index 199afe59f357..a85bc43f4344 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -1314,10 +1314,12 @@ int bind_interdomain_evtchn_to_irq_lateeoi(struct xenbus_device *dev,
>   }
>   EXPORT_SYMBOL_GPL(bind_interdomain_evtchn_to_irq_lateeoi);
>   
> -static int find_virq(unsigned int virq, unsigned int cpu, evtchn_port_t *evtchn)
> +static int find_virq(unsigned int virq, unsigned int cpu, evtchn_port_t *evtchn,
> +		     bool percpu)
>   {
>   	struct evtchn_status status;
>   	evtchn_port_t port;
> +	bool exists = false;
>   	int rc;
>   
>   	memset(&status, 0, sizeof(status));
> @@ -1329,12 +1331,16 @@ static int find_virq(unsigned int virq, unsigned int cpu, evtchn_port_t *evtchn)
>   			continue;
>   		if (status.status != EVTCHNSTAT_virq)
>   			continue;
> -		if (status.u.virq == virq && status.vcpu == xen_vcpu_nr(cpu)) {
> +		if (status.u.virq != virq)
> +			continue;
> +		if (status.vcpu == xen_vcpu_nr(cpu)) {
>   			*evtchn = port;
>   			return 0;
> +		} else if (!percpu) {
> +			exists = true;
>   		}
>   	}
> -	return -ENOENT;
> +	return exists ? -EEXIST : -ENOENT;
>   }
>   
>   /**
> @@ -1381,8 +1387,9 @@ int bind_virq_to_irq(unsigned int virq, unsigned int cpu, bool percpu)
>   			evtchn = bind_virq.port;
>   		else {
>   			if (ret == -EEXIST)
> -				ret = find_virq(virq, cpu, &evtchn);
> -			BUG_ON(ret < 0);
> +				ret = find_virq(virq, cpu, &evtchn, percpu);
> +			if (ret)
> +				goto out;

I think you are leaking info here. I guess a call of __unbind_from_irq() is
wanted like in the error case below (note that the case of no valid evtchn is
handled there just fine).


Juergen

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