From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Tan, Jianfeng" <jianfeng.tan@intel.com>
Subject: Re: [PATCH v2 5/7] net/virtio_user: add vhost kernel
	support
Date: Wed, 4 Jan 2017 15:22:08 +0800
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To: Yuanhan Liu <yuanhan.liu@linux.intel.com>
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Sorry, I forget to reply this comment.

On 12/26/2016 3:44 PM, Yuanhan Liu wrote:
> [...]
>> +
>> +	/* Does not work when VIRTIO_F_IOMMU_PLATFORM now, why? */
> Because this feature need the vhost IOTLB support from the device
> emulation. Patches for QEMU hasn't been merged yet, but it has been
> there for a while.

Yes. And it's in need of help from QEMU.

>
> Since we don't have the support yet, for sure it won't work. But
> I'm wondering why you have to disable it explicitly?

Here we do not have QEMU. Frontend driver talks with vhost-net through 
virtio_user_dev. And both ends claim to support VIRTIO_F_IOMMU_PLATFORM. 
So this feature bit will be negotiated if we don't explicitly disable 
it. In my previous test, it fails in vhost_init_device_iotlb() of vhost 
kernel module. My guess is that, for this feature, without the help of 
QEMU, vhost kernel module cannot work independently.

Thanks,
Jianfeng