Date:   Wed, 9 Mar 2022 15:55:44 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc:     Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        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>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...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>,
        Johannes Berg <johannes.berg@...el.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-um@...ts.infradead.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
Subject: Re: [PATCH v7 09/26] virtio_ring: split: implement
 virtqueue_reset_vring_split()


在 2022/3/8 下午8:35, Xuan Zhuo 写道:
> virtio ring supports reset.
>
> Queue reset is divided into several stages.
>
> 1. notify device queue reset
> 2. vring release
> 3. attach new vring
> 4. notify device queue re-enable
>
> After the first step is completed, the vring reset operation can be
> performed. If the newly set vring num does not change, then just reset
> the vq related value.
>
> Otherwise, the vring will be released and the vring will be reallocated.
> And the vring will be attached to the vq. If this process fails, the
> function will exit, and the state of the vq will be the vring release
> state. You can call this function again to reallocate the vring.
>
> In addition, vring_align, may_reduce_num are necessary for reallocating
> vring, so they are retained when creating vq.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>   drivers/virtio/virtio_ring.c | 69 ++++++++++++++++++++++++++++++++++++
>   1 file changed, 69 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index e0422c04c903..148fb1fd3d5a 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -158,6 +158,12 @@ struct vring_virtqueue {
>   			/* DMA address and size information */
>   			dma_addr_t queue_dma_addr;
>   			size_t queue_size_in_bytes;
> +
> +			/* The parameters for creating vrings are reserved for
> +			 * creating new vrings when enabling reset queue.
> +			 */
> +			u32 vring_align;
> +			bool may_reduce_num;
>   		} split;
>   
>   		/* Available for packed ring */
> @@ -217,6 +223,12 @@ struct vring_virtqueue {
>   #endif
>   };
>   
> +static void vring_free(struct virtqueue *vq);
> +static void __vring_virtqueue_init_split(struct vring_virtqueue *vq,
> +					 struct virtio_device *vdev);
> +static int __vring_virtqueue_attach_split(struct vring_virtqueue *vq,
> +					  struct virtio_device *vdev,
> +					  struct vring vring);
>   
>   /*
>    * Helpers.
> @@ -1012,6 +1024,8 @@ static struct virtqueue *vring_create_virtqueue_split(
>   		return NULL;
>   	}
>   
> +	to_vvq(vq)->split.vring_align = vring_align;
> +	to_vvq(vq)->split.may_reduce_num = may_reduce_num;
>   	to_vvq(vq)->split.queue_dma_addr = vring.dma_addr;
>   	to_vvq(vq)->split.queue_size_in_bytes = vring.queue_size_in_bytes;
>   	to_vvq(vq)->we_own_ring = true;
> @@ -1019,6 +1033,59 @@ static struct virtqueue *vring_create_virtqueue_split(
>   	return vq;
>   }
>   
> +static int virtqueue_reset_vring_split(struct virtqueue *_vq, u32 num)
> +{


So what this function does is to resize the virtqueue actually, I 
suggest to rename it as virtqueue_resize_split().


> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct virtio_device *vdev = _vq->vdev;
> +	struct vring_split vring;
> +	int err;
> +
> +	if (num > _vq->num_max)
> +		return -E2BIG;
> +
> +	switch (vq->vq.reset) {
> +	case VIRTIO_VQ_RESET_STEP_NONE:
> +		return -ENOENT;
> +
> +	case VIRTIO_VQ_RESET_STEP_VRING_ATTACH:
> +	case VIRTIO_VQ_RESET_STEP_DEVICE:
> +		if (vq->split.vring.num == num || !num)
> +			break;
> +
> +		vring_free(_vq);
> +
> +		fallthrough;
> +
> +	case VIRTIO_VQ_RESET_STEP_VRING_RELEASE:
> +		if (!num)
> +			num = vq->split.vring.num;
> +
> +		err = vring_create_vring_split(&vring, vdev,
> +					       vq->split.vring_align,
> +					       vq->weak_barriers,
> +					       vq->split.may_reduce_num, num);
> +		if (err)
> +			return -ENOMEM;


We'd better need a safe fallback here like:

If we can't allocate new memory, we can keep using the current one. 
Otherwise an ethtool -G fail may make the device not usable.

This could be done by not freeing the old vring and virtqueue states 
until new is allocated.


> +
> +		err = __vring_virtqueue_attach_split(vq, vdev, vring.vring);
> +		if (err) {
> +			vring_free_queue(vdev, vring.queue_size_in_bytes,
> +					 vring.queue,
> +					 vring.dma_addr);
> +			return -ENOMEM;
> +		}
> +
> +		vq->split.queue_dma_addr = vring.dma_addr;
> +		vq->split.queue_size_in_bytes = vring.queue_size_in_bytes;
> +	}
> +
> +	__vring_virtqueue_init_split(vq, vdev);
> +	vq->we_own_ring = true;


This seems wrong, we have the transport (rproc/mlxtbf) that allocate the 
vring by themselves. I think we need to fail the resize for we_own_ring 
== false.

Thanks



> +	vq->vq.reset = VIRTIO_VQ_RESET_STEP_VRING_ATTACH;
> +
> +	return 0;
> +}
> +
>   
>   /*
>    * Packed ring specific functions - *_packed().
> @@ -2317,6 +2384,8 @@ static int __vring_virtqueue_attach_split(struct vring_virtqueue *vq,
>   static void __vring_virtqueue_init_split(struct vring_virtqueue *vq,
>   					 struct virtio_device *vdev)
>   {
> +	vq->vq.reset = VIRTIO_VQ_RESET_STEP_NONE;
> +
>   	vq->packed_ring = false;
>   	vq->we_own_ring = false;
>   	vq->broken = false;

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