linux-kernel - [PATCH V2 1/2] xen: evtchn: Allow shared registration of IRQ handers

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Date:   Thu,  5 Oct 2023 15:55:11 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        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: [PATCH V2 1/2] xen: evtchn: Allow shared registration of IRQ handers

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 | 3 ++-
 drivers/xen/evtchn.c             | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index c7715f8bd452..d72fb26cc051 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -1238,7 +1238,8 @@ static int bind_evtchn_to_irq_chip(evtchn_port_t evtchn, struct irq_chip *chip,
 		bind_evtchn_to_cpu(evtchn, 0, false);
 	} else {
 		struct irq_info *info = info_for_irq(irq);
-		WARN_ON(info == NULL || info->type != IRQT_EVTCHN);
+		if (!WARN_ON(!info || info->type != IRQT_EVTCHN))
+			info->refcnt++;
 	}
 
 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;
-- 
2.31.1.272.g89b43f80a514