Date:   Wed, 23 Dec 2020 17:05:21 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xie Yongji <xieyongji@...edance.com>, mst@...hat.com,
        stefanha@...hat.com, sgarzare@...hat.com, parav@...dia.com,
        akpm@...ux-foundation.org, rdunlap@...radead.org,
        willy@...radead.org, viro@...iv.linux.org.uk, axboe@...nel.dk,
        bcrl@...ck.org, corbet@....net
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC v2 09/13] vduse: Add support for processing vhost iotlb
 message


On 2020/12/22 下午10:52, Xie Yongji wrote:
> To support vhost-vdpa bus driver, we need a way to share the
> vhost-vdpa backend process's memory with the userspace VDUSE process.
>
> This patch tries to make use of the vhost iotlb message to achieve
> that. We will get the shm file from the iotlb message and pass it
> to the userspace VDUSE process.
>
> Signed-off-by: Xie Yongji <xieyongji@...edance.com>
> ---
>   Documentation/driver-api/vduse.rst |  15 +++-
>   drivers/vdpa/vdpa_user/vduse_dev.c | 147 ++++++++++++++++++++++++++++++++++++-
>   include/uapi/linux/vduse.h         |  11 +++
>   3 files changed, 171 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/driver-api/vduse.rst b/Documentation/driver-api/vduse.rst
> index 623f7b040ccf..48e4b1ba353f 100644
> --- a/Documentation/driver-api/vduse.rst
> +++ b/Documentation/driver-api/vduse.rst
> @@ -46,13 +46,26 @@ The following types of messages are provided by the VDUSE framework now:
>   
>   - VDUSE_GET_CONFIG: Read from device specific configuration space
>   
> +- VDUSE_UPDATE_IOTLB: Update the memory mapping in device IOTLB
> +
> +- VDUSE_INVALIDATE_IOTLB: Invalidate the memory mapping in device IOTLB
> +
>   Please see include/linux/vdpa.h for details.
>   
> -In the data path, VDUSE framework implements a MMU-based on-chip IOMMU
> +The data path of userspace vDPA device is implemented in different ways
> +depending on the vdpa bus to which it is attached.
> +
> +In virtio-vdpa case, VDUSE framework implements a MMU-based on-chip IOMMU
>   driver which supports mapping the kernel dma buffer to a userspace iova
>   region dynamically. The userspace iova region can be created by passing
>   the userspace vDPA device fd to mmap(2).
>   
> +In vhost-vdpa case, the dma buffer is reside in a userspace memory region
> +which will be shared to the VDUSE userspace processs via the file
> +descriptor in VDUSE_UPDATE_IOTLB message. And the corresponding address
> +mapping (IOVA of dma buffer <-> VA of the memory region) is also included
> +in this message.
> +
>   Besides, the eventfd mechanism is used to trigger interrupt callbacks and
>   receive virtqueue kicks in userspace. The following ioctls on the userspace
>   vDPA device fd are provided to support that:
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index b974333ed4e9..d24aaacb6008 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -34,6 +34,7 @@
>   
>   struct vduse_dev_msg {
>   	struct vduse_dev_request req;
> +	struct file *iotlb_file;
>   	struct vduse_dev_response resp;
>   	struct list_head list;
>   	wait_queue_head_t waitq;
> @@ -325,12 +326,80 @@ static int vduse_dev_set_vq_state(struct vduse_dev *dev,
>   	return ret;
>   }
>   
> +static int vduse_dev_update_iotlb(struct vduse_dev *dev, struct file *file,
> +				u64 offset, u64 iova, u64 size, u8 perm)
> +{
> +	struct vduse_dev_msg *msg;
> +	int ret;
> +
> +	if (!size)
> +		return -EINVAL;
> +
> +	msg = vduse_dev_new_msg(dev, VDUSE_UPDATE_IOTLB);
> +	msg->req.size = sizeof(struct vduse_iotlb);
> +	msg->req.iotlb.offset = offset;
> +	msg->req.iotlb.iova = iova;
> +	msg->req.iotlb.size = size;
> +	msg->req.iotlb.perm = perm;
> +	msg->req.iotlb.fd = -1;
> +	msg->iotlb_file = get_file(file);
> +
> +	ret = vduse_dev_msg_sync(dev, msg);


My feeling is that we should provide consistent API for the userspace 
device to use.

E.g we'd better carry the IOTLB message for both virtio/vhost drivers.

It looks to me for virtio drivers we can still use UPDAT_IOTLB message 
by using VDUSE file as msg->iotlb_file here.


> +	vduse_dev_msg_put(msg);
> +	fput(file);
> +
> +	return ret;
> +}
> +
> +static int vduse_dev_invalidate_iotlb(struct vduse_dev *dev,
> +					u64 iova, u64 size)
> +{
> +	struct vduse_dev_msg *msg;
> +	int ret;
> +
> +	if (!size)
> +		return -EINVAL;
> +
> +	msg = vduse_dev_new_msg(dev, VDUSE_INVALIDATE_IOTLB);
> +	msg->req.size = sizeof(struct vduse_iotlb);
> +	msg->req.iotlb.iova = iova;
> +	msg->req.iotlb.size = size;
> +
> +	ret = vduse_dev_msg_sync(dev, msg);
> +	vduse_dev_msg_put(msg);
> +
> +	return ret;
> +}
> +
> +static unsigned int perm_to_file_flags(u8 perm)
> +{
> +	unsigned int flags = 0;
> +
> +	switch (perm) {
> +	case VHOST_ACCESS_WO:
> +		flags |= O_WRONLY;
> +		break;
> +	case VHOST_ACCESS_RO:
> +		flags |= O_RDONLY;
> +		break;
> +	case VHOST_ACCESS_RW:
> +		flags |= O_RDWR;
> +		break;
> +	default:
> +		WARN(1, "invalidate vhost IOTLB permission\n");
> +		break;
> +	}
> +
> +	return flags;
> +}
> +
>   static ssize_t vduse_dev_read_iter(struct kiocb *iocb, struct iov_iter *to)
>   {
>   	struct file *file = iocb->ki_filp;
>   	struct vduse_dev *dev = file->private_data;
>   	struct vduse_dev_msg *msg;
> -	int size = sizeof(struct vduse_dev_request);
> +	unsigned int flags;
> +	int fd, size = sizeof(struct vduse_dev_request);
>   	ssize_t ret = 0;
>   
>   	if (iov_iter_count(to) < size)
> @@ -349,6 +418,18 @@ static ssize_t vduse_dev_read_iter(struct kiocb *iocb, struct iov_iter *to)
>   		if (ret)
>   			return ret;
>   	}
> +
> +	if (msg->req.type == VDUSE_UPDATE_IOTLB && msg->req.iotlb.fd == -1) {
> +		flags = perm_to_file_flags(msg->req.iotlb.perm);
> +		fd = get_unused_fd_flags(flags);
> +		if (fd < 0) {
> +			vduse_dev_enqueue_msg(dev, msg, &dev->send_list);
> +			return fd;
> +		}
> +		fd_install(fd, get_file(msg->iotlb_file));
> +		msg->req.iotlb.fd = fd;
> +	}
> +
>   	ret = copy_to_iter(&msg->req, size, to);
>   	if (ret != size) {
>   		vduse_dev_enqueue_msg(dev, msg, &dev->send_list);
> @@ -565,6 +646,69 @@ static void vduse_vdpa_set_config(struct vdpa_device *vdpa, unsigned int offset,
>   	vduse_dev_set_config(dev, offset, buf, len);
>   }
>   
> +static void vduse_vdpa_invalidate_iotlb(struct vduse_dev *dev,
> +					struct vhost_iotlb_msg *msg)
> +{
> +	vduse_dev_invalidate_iotlb(dev, msg->iova, msg->size);
> +}
> +
> +static int vduse_vdpa_update_iotlb(struct vduse_dev *dev,
> +					struct vhost_iotlb_msg *msg)
> +{
> +	u64 uaddr = msg->uaddr;
> +	u64 iova = msg->iova;
> +	u64 size = msg->size;
> +	u64 offset;
> +	struct vm_area_struct *vma;
> +	int ret;
> +
> +	while (uaddr < msg->uaddr + msg->size) {
> +		vma = find_vma(current->mm, uaddr);
> +		ret = -EINVAL;
> +		if (!vma)
> +			goto err;
> +
> +		size = min(msg->size, vma->vm_end - uaddr);
> +		offset = (vma->vm_pgoff << PAGE_SHIFT) + uaddr - vma->vm_start;
> +		if (vma->vm_file && (vma->vm_flags & VM_SHARED)) {
> +			ret = vduse_dev_update_iotlb(dev, vma->vm_file, offset,
> +							iova, size, msg->perm);
> +			if (ret)
> +				goto err;


My understanding is that vma is something that should not be known by a 
device. So I suggest to move the above processing to vhost-vdpa.c.

Thanks


> +		}
> +		iova += size;
> +		uaddr += size;
> +	}
> +	return 0;
> +err:
> +	vduse_dev_invalidate_iotlb(dev, msg->iova, iova - msg->iova);
> +	return ret;
> +}
> +
> +static int vduse_vdpa_process_iotlb_msg(struct vdpa_device *vdpa,
> +					struct vhost_iotlb_msg *msg)
> +{
> +	struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> +	int ret = 0;
> +
> +	switch (msg->type) {
> +	case VHOST_IOTLB_UPDATE:
> +		ret = vduse_vdpa_update_iotlb(dev, msg);
> +		break;
> +	case VHOST_IOTLB_INVALIDATE:
> +		vduse_vdpa_invalidate_iotlb(dev, msg);
> +		break;
> +	case VHOST_IOTLB_BATCH_BEGIN:
> +	case VHOST_IOTLB_BATCH_END:
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
>   static void vduse_vdpa_free(struct vdpa_device *vdpa)
>   {
>   	struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> @@ -597,6 +741,7 @@ static const struct vdpa_config_ops vduse_vdpa_config_ops = {
>   	.set_status		= vduse_vdpa_set_status,
>   	.get_config		= vduse_vdpa_get_config,
>   	.set_config		= vduse_vdpa_set_config,
> +	.process_iotlb_msg	= vduse_vdpa_process_iotlb_msg,
>   	.free			= vduse_vdpa_free,
>   };
>   
> diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
> index 873305dfd93f..c5080851f140 100644
> --- a/include/uapi/linux/vduse.h
> +++ b/include/uapi/linux/vduse.h
> @@ -21,6 +21,8 @@ enum vduse_req_type {
>   	VDUSE_GET_STATUS,
>   	VDUSE_SET_CONFIG,
>   	VDUSE_GET_CONFIG,
> +	VDUSE_UPDATE_IOTLB,
> +	VDUSE_INVALIDATE_IOTLB,
>   };
>   
>   struct vduse_vq_num {
> @@ -51,6 +53,14 @@ struct vduse_dev_config_data {
>   	__u8 data[VDUSE_CONFIG_DATA_LEN];
>   };
>   
> +struct vduse_iotlb {
> +	__u32 fd;
> +	__u64 offset;
> +	__u64 iova;
> +	__u64 size;
> +	__u8 perm;
> +};
> +
>   struct vduse_dev_request {
>   	__u32 type; /* request type */
>   	__u32 unique; /* request id */
> @@ -62,6 +72,7 @@ struct vduse_dev_request {
>   		struct vduse_vq_ready vq_ready; /* virtqueue ready status */
>   		struct vduse_vq_state vq_state; /* virtqueue state */
>   		struct vduse_dev_config_data config; /* virtio device config space */
> +		struct vduse_iotlb iotlb; /* iotlb message */
>   		__u64 features; /* virtio features */
>   		__u8 status; /* device status */
>   	};

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