FAILED: patch "[PATCH] xen/events: Return -EEXIST for bound VIRQs" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 07ce121d93a5e5fb2440a24da3dbf408fcee978e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025101625-gully-disaster-8717@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 07ce121d93a5e5fb2440a24da3dbf408fcee978e Mon Sep 17 00:00:00 2001
From: Jason Andryuk <[email protected]>
Date: Wed, 27 Aug 2025 20:36:02 -0400
Subject: [PATCH] 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.

Message-ID: <[email protected]>

index 374231d84e4f..b060b5a95f45 100644
@@ -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;
 
 	memset(&status, 0, sizeof(status));
 	for (port = 0; port < xen_evtchn_max_channels(); port++) {

@@ -1330,12 +1332,16 @@ 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;
 }
 
 /**

@@ -1382,8 +1388,11 @@ 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) {
+				__unbind_from_irq(info, info->irq);
+				goto out;
+			}
 		}
 
 		ret = xen_irq_info_virq_setup(info, cpu, evtchn, virq);