kvm/eventfd: Drain events from eventfd in irqfd_wakeup()

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

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20201027135523.646811-4-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index efa8a5ae7a95f2f65c010e51e0d9b845e929fd2b..e996989cd580e76e058a712dd8e0967b4909ccea 100644 (file)
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -194,6 +194,9 @@ irqfd_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
        int ret = 0;
 
        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);