linux-kernel - [PATCH 3/3] kvm/eventfd: Drain events from eventfd in irqfd

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Message-Id: <20201027135523.646811-4-dwmw2@infradead.org>
Date:   Tue, 27 Oct 2020 13:55:23 +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 3/3] kvm/eventfd: Drain events from eventfd in irqfd_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>
---
 virt/kvm/eventfd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index d6408bb497dc..98b5cfa1d69f 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -193,6 +193,9 @@ irqfd_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
 	int idx;
 
 	if (flags & EPOLLIN) {
+		u64 cnt;
+		eventfd_ctx_do_read(&irqfd->eventfd, &cnt);
+
 		idx = srcu_read_lock(&kvm->irq_srcu);
 		do {
 			seq = read_seqcount_begin(&irqfd->irq_entry_sc);
-- 
2.26.2