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Subject: Re: [PATCH v7 2/3] uacce: add uacce driver
To:     Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        jonathan.cameron@huawei.com, grant.likely@arm.com,
        Jerome Glisse <jglisse@redhat.com>,
        ilias.apalodimas@linaro.org, francois.ozog@linaro.org,
        kenneth-lee-2012@foxmail.com, Wangzhou <wangzhou1@hisilicon.com>,
        "haojian . zhuang" <haojian.zhuang@linaro.org>,
        guodong.xu@linaro.org, linux-accelerators@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        iommu@lists.linux-foundation.org,
        Kenneth Lee <liguozhu@hisilicon.com>,
        Zaibo Xu <xuzaibo@huawei.com>
References: <1572331216-9503-1-git-send-email-zhangfei.gao@linaro.org>
 <1572331216-9503-3-git-send-email-zhangfei.gao@linaro.org>
 <20191105114844.GA3648434@lophozonia>
From:   zhangfei <zhangfei.gao@linaro.org>
Message-ID: <24cbcd55-56d0-83b9-6284-04c29da11306@linaro.org>
Date:   Wed, 6 Nov 2019 16:17:40 +0800
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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