linux-kernel - [PATCH 2/3] vfio/virqfd: Drain events from eventfd in virqfd

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Date:   Tue, 27 Oct 2020 13:55:22 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     bonzini@...hat.com
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH 2/3] vfio/virqfd: Drain events from eventfd in virqfd_wakeup()

From: David Woodhouse <dwmw@...zon.co.uk>

Don't allow the events to accumulate in the eventfd counter, drain them
as they are handled.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 drivers/vfio/virqfd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/vfio/virqfd.c b/drivers/vfio/virqfd.c
index 997cb5d0a657..414e98d82b02 100644
--- a/drivers/vfio/virqfd.c
+++ b/drivers/vfio/virqfd.c
@@ -46,6 +46,9 @@ static int virqfd_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync, void
 	__poll_t flags = key_to_poll(key);
 
 	if (flags & EPOLLIN) {
+		u64 cnt;
+		eventfd_ctx_do_read(virqfd->eventfd, &cnt);
+
 		/* An event has been signaled, call function */
 		if ((!virqfd->handler ||
 		     virqfd->handler(virqfd->opaque, virqfd->data)) &&
-- 
2.26.2