linux-kernel - Re: [PATCH 1/2] xen: evtchn: Allow shared registration of IRQ handers

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Date:   Thu, 28 Sep 2023 17:33:08 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Alex Bennée <alex.bennee@...aro.org>,
        stratos-dev@...lists.linaro.org,
        Erik Schilling <erik.schilling@...aro.org>,
        Manos Pitsidianakis <manos.pitsidianakis@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] xen: evtchn: Allow shared registration of IRQ handers

On 29.08.23 14:29, Viresh Kumar wrote:
> Currently the handling of events is supported either in the kernel or
> userspace, but not both.
> 
> In order to support fast delivery of interrupts from the guest to the
> backend, we need to handle the Queue notify part of Virtio protocol in
> kernel and the rest in userspace.
> 
> Update the interrupt handler registration flag to IRQF_SHARED for event
> channels, which would allow multiple entities to bind their interrupt
> handler for the same event channel port.
> 
> Also increment the reference count of irq_info when multiple entities
> try to bind event channel to irqchip, so the unbinding happens only
> after all the users are gone.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>   drivers/xen/events/events_base.c | 1 +
>   drivers/xen/evtchn.c             | 2 +-
>   2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index c7715f8bd452..0182680dab3a 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -1239,6 +1239,7 @@ static int bind_evtchn_to_irq_chip(evtchn_port_t evtchn, struct irq_chip *chip,
>   	} else {
>   		struct irq_info *info = info_for_irq(irq);
>   		WARN_ON(info == NULL || info->type != IRQT_EVTCHN);
> +		info->refcnt++;

This should be conditional on the WARN_ON() not triggering.

>   	}
>   
>   out:
> diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
> index c99415a70051..43f77915feb5 100644
> --- a/drivers/xen/evtchn.c
> +++ b/drivers/xen/evtchn.c
> @@ -397,7 +397,7 @@ static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port)
>   	if (rc < 0)
>   		goto err;
>   
> -	rc = bind_evtchn_to_irqhandler_lateeoi(port, evtchn_interrupt, 0,
> +	rc = bind_evtchn_to_irqhandler_lateeoi(port, evtchn_interrupt, IRQF_SHARED,
>   					       u->name, evtchn);
>   	if (rc < 0)
>   		goto err;


Juergen

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