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

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Date: Tue, 7 May 2024 21:22:42 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: 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 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?

> +
> +		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.

> +
> +		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)

Jason