D19501.id.diff
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D19501.id.diff
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	Index: head/usr.sbin/bhyve/virtio.c
	===================================================================
	--- head/usr.sbin/bhyve/virtio.c
	+++ head/usr.sbin/bhyve/virtio.c
	@@ -3,6 +3,7 @@
	*
	* Copyright (c) 2013 Chris Torek <torek @ torek net>
	* All rights reserved.
	+ * Copyright (c) 2019 Joyent, Inc.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	@@ -32,6 +33,8 @@
	#include <sys/param.h>
	#include <sys/uio.h>

	+#include <machine/atomic.h>
	+
	#include <stdio.h>
	#include <stdint.h>
	#include <pthread.h>
	@@ -422,6 +425,12 @@
	vue = &vuh->vu_ring[uidx++ & mask];
	vue->vu_idx = idx;
	vue->vu_tlen = iolen;
	+
	+ /*
	+ * Ensure the used descriptor is visible before updating the index.
	+ * This is necessary on ISAs with memory ordering less strict than x86.
	+ */
	+ atomic_thread_fence_rel();
	vuh->vu_idx = uidx;
	}

	@@ -459,6 +468,13 @@
	vs = vq->vq_vs;
	old_idx = vq->vq_save_used;
	vq->vq_save_used = new_idx = vq->vq_used->vu_idx;
	+
	+ /*
	+ * Use full memory barrier between vu_idx store from preceding
	+ * vq_relchain() call and the loads from VQ_USED_EVENT_IDX() or
	+ * va_flags below.
	+ */
	+ atomic_thread_fence_seq_cst();
	if (used_all_avail &&
	(vs->vs_negotiated_caps & VIRTIO_F_NOTIFY_ON_EMPTY))
	intr = 1;