netdev - Re: [PATCH v11 21/40] virtio_ring: packed: introduce virtqueue_resize

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Date:   Mon, 4 Jul 2022 12:02:35 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Vadim Pasternak <vadimp@...dia.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Eric Farman <farman@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-um@...ts.infradead.org, netdev@...r.kernel.org,
        platform-driver-x86@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, bpf@...r.kernel.org,
        kangjie.xu@...ux.alibaba.com,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v11 21/40] virtio_ring: packed: introduce
 virtqueue_resize_packed()


在 2022/7/4 10:13, Xuan Zhuo 写道:
> On Fri, 1 Jul 2022 17:27:48 +0800, Jason Wang <jasowang@...hat.com> wrote:
>> 在 2022/6/29 14:56, Xuan Zhuo 写道:
>>> virtio ring packed supports resize.
>>>
>>> Only after the new vring is successfully allocated based on the new num,
>>> we will release the old vring. In any case, an error is returned,
>>> indicating that the vring still points to the old vring.
>>>
>>> In the case of an error, re-initialize(by virtqueue_reinit_packed()) the
>>> virtqueue to ensure that the vring can be used.
>>>
>>> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>>> ---
>>>    drivers/virtio/virtio_ring.c | 29 +++++++++++++++++++++++++++++
>>>    1 file changed, 29 insertions(+)
>>>
>>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>>> index 650f701a5480..4860787286db 100644
>>> --- a/drivers/virtio/virtio_ring.c
>>> +++ b/drivers/virtio/virtio_ring.c
>>> @@ -2042,6 +2042,35 @@ static struct virtqueue *vring_create_virtqueue_packed(
>>>    	return NULL;
>>>    }
>>>
>>> +static int virtqueue_resize_packed(struct virtqueue *_vq, u32 num)
>>> +{
>>> +	struct vring_virtqueue_packed vring = {};
>>> +	struct vring_virtqueue *vq = to_vvq(_vq);
>>> +	struct virtio_device *vdev = _vq->vdev;
>>> +	int err;
>>> +
>>> +	if (vring_alloc_queue_packed(&vring, vdev, num))
>>> +		goto err_ring;
>>> +
>>> +	err = vring_alloc_state_extra_packed(&vring);
>>> +	if (err)
>>> +		goto err_state_extra;
>>> +
>>> +	vring_free(&vq->vq);
>>> +
>>> +	virtqueue_init(vq, vring.vring.num);
>>> +	virtqueue_vring_attach_packed(vq, &vring);
>>> +	virtqueue_vring_init_packed(vq);
>>> +
>>> +	return 0;
>>> +
>>> +err_state_extra:
>>> +	vring_free_packed(&vring, vdev);
>>> +err_ring:
>>> +	virtqueue_reinit_packed(vq);
>>
>> So desc_state and desc_extra has been freed vring_free_packed() when
>> vring_alloc_state_extra_packed() fails. We might get use-after-free here?
> vring_free_packed() frees the temporary structure vring. It does not affect
> desc_state and desc_extra of vq. So it is safe.


You are right.


>
>> Actually, I think for resize we need
>>
>> 1) detach old
>> 2) allocate new
>> 3) if 2) succeed, attach new otherwise attach old
>
> The implementation is now:
>
> 1. allocate new
> 2. free old (detach old)
> 3. attach new
>
> error:
> 1. free temporary
> 2. reinit old
>
> Do you think this is ok? We need to add a new variable to save the old vring in
> the process you mentioned, there is not much difference in other.


Yes, I think the code is fine. But I'd suggest to rename "vring" to 
"vring_packed", this simplify the reviewers.

Other than this, you can add:

Acked-by: Jason Wang <jasowang@...hat.com>


>
> Thanks.
>
>
>> This seems more clearer than the current logic?
>>
>> Thanks
>>
>>
>>> +	return -ENOMEM;
>>> +}
>>> +
>>>
>>>    /*
>>>     * Generic functions and exported symbols.