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Subject: Re: [PATCH net-next v1 4/5] virtio_ring: add event idx support in
 packed ring
To:     Tiwei Bie <tiwei.bie@intel.com>, mst@redhat.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        virtio-dev@lists.oasis-open.org
Cc:     wexu@redhat.com, jfreimann@redhat.com
References: <20180709072241.8886-1-tiwei.bie@intel.com>
 <20180709072241.8886-5-tiwei.bie@intel.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <9ee31221-9f4a-f1c5-0f0b-8d178bb536e9@redhat.com>
Date:   Tue, 10 Jul 2018 13:50:03 +0800
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On 2018年07月09日 15:22, Tiwei Bie wrote:
> @@ -1059,9 +1059,19 @@ static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
>   	 * suppressions. */
>   	virtio_mb(vq->weak_barriers);
>   
> +	old = vq->next_avail_idx - vq->num_added;
> +	new = vq->next_avail_idx;
> +	vq->num_added = 0;
> +
>   	snapshot = *(u32 *)vq->vring_packed.device;

I think we should use READ_ONCE() to prevent compiler from re-reading.

> +	off_wrap = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot & 0xffff));
>   	flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3;
>   
> +	wrap_counter = off_wrap >> 15;
> +	event_idx = off_wrap & ~(1 << 15);
> +	if (wrap_counter != vq->avail_wrap_counter)
> +		event_idx -= vq->vring_packed.num;

Thanks