Re: [PATCH v7 2/3] uacce: add uacce driver

[zhangfei <zhangfei.gao@linaro.org>]

Hi, Jean

Thanks for the review.

On 2019/11/5 下午7:48, Jean-Philippe Brucker wrote:
> Hi Zhangfei,
>
> Thanks for simplifying this, it's a lot easier to review. I have some
> additional comments.
>
> On Tue, Oct 29, 2019 at 02:40:15PM +0800, Zhangfei Gao wrote:
>> +static int uacce_sva_exit(struct device *dev, struct iommu_sva *handle,
>> +			  void *data)
>> +{
>> +	struct uacce_device *uacce = data;
>> +	struct uacce_queue *q;
>> +
>> +	mutex_lock(&uacce->q_lock);
>> +	list_for_each_entry(q, &uacce->qs, list) {
>> +		if (q->pid == task_pid_nr(current))
>> +			uacce_put_queue(q);
> This won't work in some cases, because any thread can call __mmput() and
> end up here. For example a sibling thread that inherited the queue, or a
> workqueue that's executing mmput_async_fn(). In addition I think comparing
> PID values is unsafe (see comment in pid.h), we'd need to use the struct
> pid if we wanted to do it this way.
OK, still in check.
>
> But I still believe it would be better to create an uacce_mm structure
> that tracks all queues bound to this mm, and pass that to uacce_sva_exit
> instead of the uacce_device.
I am afraid this method may not work.
Since currently iommu_sva_bind_device only accept the same drvdata for 
the same dev,
that's the reason we can not directly use "queue" as drvdata.
Each time create an uacce_mm structure should be same problem as queue, 
and fail for same dev.
So we use uacce and pick up the right queue inside.

>
> The queue isn't bound to a task, but its address space. With clone() the
> address space can be shared between tasks. In addition, whoever has a
> queue fd also gets access to this address space. So after a fork() the
> child may be able to program the queue to DMA into the parent's address
> space, even without CLONE_VM. Users must be aware of this and I think it's
> important to explain it very clearly in the UAPI.
>
> [...]
>> +static struct uacce_qfile_region *
>> +uacce_create_region(struct uacce_queue *q, struct vm_area_struct *vma,
>> +		    enum uacce_qfrt type, unsigned int flags)
>> +{
>> +	struct uacce_device *uacce = q->uacce;
>> +	struct uacce_qfile_region *qfr;
>> +	int ret = -ENOMEM;
>> +
>> +	qfr = kzalloc(sizeof(*qfr), GFP_KERNEL);
>> +	if (!qfr)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	qfr->type = type;
>> +	qfr->flags = flags;
>> +
>> +	if (vma->vm_flags & VM_READ)
>> +		qfr->prot |= IOMMU_READ;
> qfr->prot and qfr->flags aren't used at the moment, you could remove them.
Yes,
>
>> +
>> +	if (vma->vm_flags & VM_WRITE)
>> +		qfr->prot |= IOMMU_WRITE;
>> +
>> +	if (flags & UACCE_QFRF_SELFMT) {
>> +		if (!uacce->ops->mmap) {
>> +			ret = -EINVAL;
>> +			goto err_with_qfr;
>> +		}
>> +
>> +		ret = uacce->ops->mmap(q, vma, qfr);
>> +		if (ret)
>> +			goto err_with_qfr;
>> +		return qfr;
>> +	}
>> +
>> +	return qfr;
>> +
>> +err_with_qfr:
>> +	kfree(qfr);
>> +	return ERR_PTR(ret);
>> +}
>> +
>> +static int uacce_fops_mmap(struct file *filep, struct vm_area_struct *vma)
>> +{
>> +	struct uacce_queue *q = filep->private_data;
>> +	struct uacce_device *uacce = q->uacce;
>> +	struct uacce_qfile_region *qfr;
>> +	enum uacce_qfrt type = 0;
>> +	unsigned int flags = 0;
>> +	int ret;
>> +
>> +	if (vma->vm_pgoff < UACCE_QFRT_MAX)
>> +		type = vma->vm_pgoff;
> Otherwise return -EINVAL?  type probably shouldn't default to MMIO if it
> wasn't explicitly requested by the user.
OK
>
>> +
>> +	vma->vm_flags |= VM_DONTCOPY | VM_DONTEXPAND | VM_WIPEONFORK;
>> +	vma->vm_ops = &uacce_vm_ops;
>> +	vma->vm_private_data = q;
>> +
>> +	mutex_lock(&uacce_mutex);
>> +
>> +	if (q->qfrs[type]) {
>> +		ret = -EEXIST;
>> +		goto out_with_lock;
>> +	}
>> +
>> +	switch (type) {
>> +	case UACCE_QFRT_MMIO:
>> +		flags = UACCE_QFRF_SELFMT;
>> +		break;
>> +
>> +	case UACCE_QFRT_DUS:
>> +		if (uacce->flags & UACCE_DEV_SVA) {
>> +			flags = UACCE_QFRF_SELFMT;
> I'd simplify this even further by getting rid of the SELFMT flag. It's the
> only possibility at the moment.
OK, we can remove this flag for simplicity, may add it back if required 
in future patch.
>
>> +			break;
>> +		}
>> +		break;
>> +
>> +	default:
>> +		WARN_ON(&uacce->dev);
> WARN_ON(uacce->dev). But shouldn't we instead return -EINVAL here?
> UACCE_QFRT_MAX is currently 16, so users can easily trigger this WARN by
> passing an invalid value.
Yes, good idea.
>
> [...]
>> +void uacce_unregister(struct uacce_device *uacce)
>> +{
>> +	if (!uacce)
>> +		return;
>> +
>> +	mutex_lock(&uacce->q_lock);
>> +	if (!list_empty(&uacce->qs)) {
>> +		struct uacce_queue *q;
>> +
>> +		list_for_each_entry(q, &uacce->qs, list) {
>> +			uacce_put_queue(q);
> The open file descriptor will still exist after this function returns.
> Can all fops can be called with a stale queue?
To more clear:.
Do you mean rmmod without fops_release.

Thanks