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Date: Tue, 12 Apr 2016 00:41:20 +0800
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: "Xie, Huawei" <huawei.xie@intel.com>
Cc: "Tao, Zhe" <zhe.tao@intel.com>, "dev@dpdk.org" <dev@dpdk.org>
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Subject: Re: [dpdk-dev] [PATCH] vhost: fix mem share between VM and host
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On Mon, Apr 11, 2016 at 06:22:12AM +0000, Xie, Huawei wrote:
> On 4/11/2016 1:29 AM, Zhe Tao wrote:
> >  
> > +/* Check the share memory in case the QEMU doesn't set the share option
> > + * as on for the memory-backend-file object in the QEMU command line.
> > + */
> > +
> > +int
> > +vhost_check_mem_shared(struct vhost_device_ctx ctx)
> > +{
> > +	struct virtio_net *dev;
> > +	struct vhost_virtqueue *vq;
> > +	int ret = 0;
> > +
> > +	dev = get_device(ctx);
> > +	if ((dev == NULL) || (dev->mem == NULL))
> > +		return -1;
> > +
> > +	/* check first virtqueue 0 rxq. */
> > +	vq = dev->virtqueue[VIRTIO_RXQ];
> > +	ret = vq->desc[0].next == 0 ? -1 : 0;
> > +
> > +	if (ret)
> > +		RTE_LOG(ERR, VHOST_CONFIG,
> > +			"The mem is not shared between VM and host\n");
> > +
> > +	return ret;
> > +}
> > +
> 
> Zhe: This is known to vhost-user users that share=on is a must-to-have
> option. I think this isn't an issue.

Agreed.

> It is OK if we could do some early check in vhost, however we couldn't

I think if there is really a need to do the check, it might should be
done in QEMU: the option is from QEMU after all.

> assume the value of vq->desc[0].next.
> Check if there is other simple and reliable way.

I will not say no to an elegant check though.

	--yliu