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

Jason Gunthorpe
2024-05-08T00:22:44Z

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