linux-kernel - [PATCH v2 7/8] xen/evtch: use smp barriers for user event ring

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Message-Id: <20210211101616.13788-8-jgross@suse.com>
Date:   Thu, 11 Feb 2021 11:16:15 +0100
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Jan Beulich <jbeulich@...e.com>
Subject: [PATCH v2 7/8] xen/evtch: use smp barriers for user event ring

The ring buffer for user events is local to the given kernel instance,
so smp barriers are fine for ensuring consistency.

Reported-by: Andrew Cooper <andrew.cooper3@...rix.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
Reviewed-by: Jan Beulich <jbeulich@...e.com>
---
 drivers/xen/evtchn.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index a7a85719a8c8..421382c73d88 100644
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -173,7 +173,7 @@ static irqreturn_t evtchn_interrupt(int irq, void *data)
 
 	if ((u->ring_prod - u->ring_cons) < u->ring_size) {
 		*evtchn_ring_entry(u, u->ring_prod) = evtchn->port;
-		wmb(); /* Ensure ring contents visible */
+		smp_wmb(); /* Ensure ring contents visible */
 		if (u->ring_cons == u->ring_prod++) {
 			wake_up_interruptible(&u->evtchn_wait);
 			kill_fasync(&u->evtchn_async_queue,
@@ -245,7 +245,7 @@ static ssize_t evtchn_read(struct file *file, char __user *buf,
 	}
 
 	rc = -EFAULT;
-	rmb(); /* Ensure that we see the port before we copy it. */
+	smp_rmb(); /* Ensure that we see the port before we copy it. */
 	if (copy_to_user(buf, evtchn_ring_entry(u, c), bytes1) ||
 	    ((bytes2 != 0) &&
 	     copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
-- 
2.26.2