linux-kernel - Re: [PATCH v5 5/9] iommufd: Add iommufd fault object

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Date: Fri, 10 May 2024 17:13:29 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Kevin Tian <kevin.tian@...el.com>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Nicolin Chen <nicolinc@...dia.com>, Yi Liu <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Joel Granados <j.granados@...sung.com>, iommu@...ts.linux.dev,
 virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 5/9] iommufd: Add iommufd fault object

On 2024/5/8 8:22, Jason Gunthorpe wrote:
> On Tue, Apr 30, 2024 at 10:57:06PM +0800, Lu Baolu wrote:
>> +static ssize_t iommufd_fault_fops_read(struct file *filep, char __user *buf,
>> +				       size_t count, loff_t *ppos)
>> +{
>> +	size_t fault_size = sizeof(struct iommu_hwpt_pgfault);
>> +	struct iommufd_fault *fault = filep->private_data;
>> +	struct iommu_hwpt_pgfault data;
>> +	struct iommufd_device *idev;
>> +	struct iopf_group *group;
>> +	struct iopf_fault *iopf;
>> +	size_t done = 0;
>> +	int rc;
>> +
>> +	if (*ppos || count % fault_size)
>> +		return -ESPIPE;
>> +
>> +	mutex_lock(&fault->mutex);
>> +	while (!list_empty(&fault->deliver) && count > done) {
>> +		group = list_first_entry(&fault->deliver,
>> +					 struct iopf_group, node);
>> +
>> +		if (list_count_nodes(&group->faults) * fault_size > count - done)
>> +			break;
> 
> Can this list_count be precomputed when we build the fault group?

Yes. Done.

> 
>> +
>> +		idev = group->attach_handle->idev;
>> +		if (!idev)
>> +			break;
> 
> This check should be done before adding the fault to the linked
> list. See my other note about the race.

Done.

> 
>> +
>> +		rc = xa_alloc(&idev->faults, &group->cookie, group,
>> +			      xa_limit_32b, GFP_KERNEL);
>> +		if (rc)
>> +			break;
> 
> This error handling is not quite right, if done == 0 then this should
> return rc.
> 
> 
>> +
>> +		list_for_each_entry(iopf, &group->faults, list) {
>> +			iommufd_compose_fault_message(&iopf->fault,
>> +						      &data, idev,
>> +						      group->cookie);
>> +			rc = copy_to_user(buf + done, &data, fault_size);
>> +			if (rc) {
>> +				xa_erase(&idev->faults, group->cookie);
>> +				break;
> 
> Same here
> 
> (same comment on the write side too)

All fixed. Thank you!

Best regards,
baolu