linux-kernel - [PATCH] xen/events: Fix Global and Domain VIRQ tracking

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Message-ID: <20250812190041.23276-1-jason.andryuk@amd.com>
Date: Tue, 12 Aug 2025 15:00:40 -0400
From: Jason Andryuk <jason.andryuk@....com>
To: Juergen Gross <jgross@...e.com>, Stefano Stabellini
	<sstabellini@...nel.org>, Oleksandr Tyshchenko
	<oleksandr_tyshchenko@...m.com>, Chris Wright <chrisw@...s-sol.org>, "Jeremy
 Fitzhardinge" <jeremy@...source.com>
CC: Jason Andryuk <jason.andryuk@....com>, <stable@...r.kernel.org>,
	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] xen/events: Fix Global and Domain VIRQ tracking

VIRQs come in 3 flavors, per-VPU, per-domain, and global.  The existing
tracking of VIRQs is handled by per-cpu variables virq_to_irq.

The issue is that bind_virq_to_irq() sets the per_cpu virq_to_irq at
registration time - typically CPU 0.  Later, the interrupt can migrate,
and info->cpu is updated.  When calling unbind_from_irq(), the per-cpu
virq_to_irq is cleared for a different cpu.  If bind_virq_to_irq() is
called again with CPU 0, the stale irq is returned.

Change the virq_to_irq tracking to use CPU 0 for per-domain and global
VIRQs.  As there can be at most one of each, there is no need for
per-vcpu tracking.  Also, per-domain and global VIRQs need to be
registered on CPU 0 and can later move, so this matches the expectation.

Fixes: e46cdb66c8fc ("xen: event channels")
Cc: stable@...r.kernel.org
Signed-off-by: Jason Andryuk <jason.andryuk@....com>
---
Fixes is the introduction of the virq_to_irq per-cpu array.

This was found with the out-of-tree argo driver during suspend/resume.
On suspend, the per-domain VIRQ_ARGO is unbound.  On resume, the driver
attempts to bind VIRQ_ARGO.  The stale irq is returned, but the
WARN_ON(info == NULL || info->type != IRQT_VIRQ) in bind_virq_to_irq()
triggers for NULL info.  The bind fails and execution continues with the
driver trying to clean up by unbinding.  This eventually faults over the
NULL info.
---
 drivers/xen/events/events_base.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 41309d38f78c..a27e4d7f061e 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -159,7 +159,19 @@ static DEFINE_MUTEX(irq_mapping_update_lock);
 
 static LIST_HEAD(xen_irq_list_head);
 
-/* IRQ <-> VIRQ mapping. */
+static bool is_per_vcpu_virq(int virq) {
+	switch (virq) {
+	case VIRQ_TIMER:
+	case VIRQ_DEBUG:
+	case VIRQ_XENOPROF:
+	case VIRQ_XENPMU:
+		return true;
+	default:
+		return false;
+	}
+}
+
+/* IRQ <-> VIRQ mapping.  Global/Domain virqs are tracked in cpu 0.  */
 static DEFINE_PER_CPU(int [NR_VIRQS], virq_to_irq) = {[0 ... NR_VIRQS-1] = -1};
 
 /* IRQ <-> IPI mapping */
@@ -974,6 +986,9 @@ static void __unbind_from_irq(struct irq_info *info, unsigned int irq)
 
 		switch (info->type) {
 		case IRQT_VIRQ:
+			if (!is_per_vcpu_virq(virq_from_irq(info)))
+				cpu = 0;
+
 			per_cpu(virq_to_irq, cpu)[virq_from_irq(info)] = -1;
 			break;
 		case IRQT_IPI:
-- 
2.50.1