linux-kernel - [PATCH 4/5] xen/events: unmask a fifo event channel only if it was masked

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Date:   Thu, 22 Oct 2020 09:42:13 +0200
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>,
        Jan Beulich <jbeulich@...e.com>
Subject: [PATCH 4/5] xen/events: unmask a fifo event channel only if it was masked

Unmasking an event channel with fifo events channels being used can
require a hypercall to be made, so try to avoid that by checking
whether the event channel was really masked.

Suggested-by: Jan Beulich <jbeulich@...e.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
---
 drivers/xen/events/events_fifo.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 243e7b6d7b96..f60c5a9ec833 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -236,6 +236,9 @@ static bool clear_masked_cond(volatile event_word_t *word)
 
 	w = *word;
 
+	if (!(w & (1 << EVTCHN_FIFO_MASKED)))
+		return true;
+
 	do {
 		if (w & (1 << EVTCHN_FIFO_PENDING))
 			return false;
-- 
2.26.2