linux-kernel - Re: [PATCH v4 2/2] mm/hmm/test: add self tests for HMM

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Date:   Tue, 12 Nov 2019 13:51:11 -0800
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Shuah Khan <shuah@...nel.org>, <linux-rdma@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] mm/hmm/test: add self tests for HMM


On 11/12/19 7:25 AM, Christoph Hellwig wrote:
> Shouldn't this go into mm/ instead? It certainly doesn't seem
> like a library.

I was following the convention for the other vm test kernel modules.
I see a couple of modules in mm/ but I don't have a personal
preference for where to place it.

Andrew, do you have a preference?

>> +static int dmirror_bounce_copy_from(struct dmirror_bounce *bounce,
>> +				    unsigned long addr)
>> +{
>> +	unsigned long end = addr + bounce->size;
>> +	char __user *uptr = (void __user *)addr;
>> +	void *ptr = bounce->ptr;
>> +
>> +	for (; addr < end; addr += PAGE_SIZE, ptr += PAGE_SIZE,
>> +					      uptr += PAGE_SIZE) {
>> +		int ret;
>> +
>> +		ret = copy_from_user(ptr, uptr, PAGE_SIZE);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>> +	return 0;
>> +}
> 
> Why does this iterate in page sized chunks?  I don't remember a page
> size limit on copy_{from,to}_user.

Good point. I'll fix that.

>> +static int dmirror_invalidate_range_start(struct mmu_notifier *mn,
>> +				const struct mmu_notifier_range *update)
>> +{
>> +	struct dmirror *dmirror = container_of(mn, struct dmirror, notifier);
>> +
>> +	if (mmu_notifier_range_blockable(update))
>> +		mutex_lock(&dmirror->mutex);
>> +	else if (!mutex_trylock(&dmirror->mutex))
>> +		return -EAGAIN;
>> +
>> +	dmirror_do_update(dmirror, update->start, update->end);
>> +	mutex_unlock(&dmirror->mutex);
>> +	return 0;
>> +}
> 
> Can we adopts this to Jasons new interval tree invalidate?

Well, it would mean registering for the whole process address space.
I'll give it a try.

>> +static int dmirror_fops_open(struct inode *inode, struct file *filp)
>> +{
>> +	struct cdev *cdev = inode->i_cdev;
>> +	struct dmirror_device *mdevice;
>> +	struct dmirror *dmirror;
>> +
>> +	/* No exclusive opens. */
>> +	if (filp->f_flags & O_EXCL)
>> +		return -EINVAL;
> 
> Device files usually just ignore O_EXCL, I don't see why this one
> would be any different.

OK, I'll remove that test.

>> +	mdevice = container_of(cdev, struct dmirror_device, cdevice);
>> +	dmirror = dmirror_new(mdevice);
>> +	if (!dmirror)
>> +		return -ENOMEM;
>> +
>> +	/* Only the first open registers the address space. */
>> +	mutex_lock(&mdevice->devmem_lock);
>> +	if (filp->private_data)
>> +		goto err_busy;
>> +	filp->private_data = dmirror;
>> +	mutex_unlock(&mdevice->devmem_lock);
> 
> ->open is only called for the first open of a given file structure..
> 
>> +static int dmirror_fops_release(struct inode *inode, struct file *filp)
>> +{
>> +	struct dmirror *dmirror = filp->private_data;
>> +
>> +	if (!dmirror)
>> +		return 0;
> 
> This can't happen if your ->open never returns 0 without setting the
> private data.
> 
>> +	filp->private_data = NULL;
> 
> The file is feed afterwards, no need to clear the private data.

OK, I'll clean that up.