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

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Message-ID: <20250826005517.41547-3-jason.andryuk@amd.com>
Date: Mon, 25 Aug 2025 20:55:14 -0400
From: Jason Andryuk <jason.andryuk@....com>
To: Juergen Gross <jgross@...e.com>, Stefano Stabellini
	<sstabellini@...nel.org>, Oleksandr Tyshchenko
	<oleksandr_tyshchenko@...m.com>
CC: Jason Andryuk <jason.andryuk@....com>, <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v2 2/3] xen/events: Return -EEXIST for bound VIRQs

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;
 		}
 
 		ret = xen_irq_info_virq_setup(info, cpu, evtchn, virq);
-- 
2.50.1