From 8d148003fdf7bd9e28137e6683ef46902af39146 Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Tue, 20 Oct 2020 14:42:52 +0200
Subject: [PATCH] evtchn/fifo: use stable fields when recording "last queue"
 information

Both evtchn->priority and evtchn->notify_vcpu_id could change behind the
back of evtchn_fifo_set_pending(), as for it - in the case of
interdomain channels - only the remote side's per-channel lock is held.
Neither the queue's priority nor the vCPU's vcpu_id fields have similar
properties, so they seem better suited for the purpose. In particular
they reflect the respective evtchn fields' values at the time they were
used to determine queue and vCPU.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Paul Durrant <paul@xen.org>
master commit: 6f6f07b64cbe90e54f8e62b4d6f2404cf5306536
master date: 2020-10-02 08:37:35 +0200
---
 xen/common/event_fifo.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c
index 68d0c7a632..27ab3a1c3f 100644
--- a/xen/common/event_fifo.c
+++ b/xen/common/event_fifo.c
@@ -225,8 +225,8 @@ static void evtchn_fifo_set_pending(struct vcpu *v, struct evtchn *evtchn)
         /* Moved to a different queue? */
         if ( old_q != q )
         {
-            evtchn->last_vcpu_id = evtchn->notify_vcpu_id;
-            evtchn->last_priority = evtchn->priority;
+            evtchn->last_vcpu_id = v->vcpu_id;
+            evtchn->last_priority = q->priority;
 
             spin_unlock_irqrestore(&old_q->lock, flags);
             spin_lock_irqsave(&q->lock, flags);
-- 
2.20.1