RE: [PATCH v6 06/10] iommufd: Add iommufd fault object

Tian, Kevin
2024-06-07T09:17:31Z

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Monday, May 27, 2024 12:05 PM
>
> +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 = 0;
> +
> + if (*ppos || count % fault_size)
> + return -ESPIPE;

the man page says:

"If count is zero, read() returns zero and has no other results."

> +
> + mutex_lock(&fault->mutex);
> + while (!list_empty(&fault->deliver) && count > done) {
> + group = list_first_entry(&fault->deliver,
> + struct iopf_group, node);
> +
> + if (group->fault_count * fault_size > count - done)
> + break;
> +
> + rc = xa_alloc(&fault->response, &group->cookie, group,
> + xa_limit_32b, GFP_KERNEL);
> + if (rc)
> + break;
> +
> + idev = to_iommufd_handle(group->attach_handle)->idev;
> + 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) {

'rc' should be converted to -EFAULT.

> + xa_erase(&fault->response, group->cookie);
> + break;
> + }
> + done += fault_size;
> + }
> +
> + list_del(&group->node);
> + }
> + mutex_unlock(&fault->mutex);
> +
> + return done == 0 ? rc : done;

again this doesn't match the manual:

"On error, -1 is returned, and errno is set appropriately. "

it doesn't matter whether 'done' is 0.

> +
> +static int iommufd_fault_fops_release(struct inode *inode, struct file *filep)
> +{
> + struct iommufd_fault *fault = filep->private_data;
> +
> + iommufd_ctx_put(fault->ictx);
> + refcount_dec(&fault->obj.users);
> + return 0;
> +}

hmm this doesn't sound correct. the context and refcount are
acquired in iommufd_fault_alloc() but here they are reverted when
the fd is closed...

> +
> + filep = anon_inode_getfile("[iommufd-pgfault]",
> &iommufd_fault_fops,
> + fault, O_RDWR);
> + if (IS_ERR(filep)) {
> + rc = PTR_ERR(filep);
> + goto out_abort;
> + }
> +
> + refcount_inc(&fault->obj.users);
> + iommufd_ctx_get(fault->ictx);
> + fault->filep = filep;

those 3 lines can be moved after below fdno get. It's reads slightly
clearer to put file related work together before getting to the last piece
of intiailzation.

> +
> + fdno = get_unused_fd_flags(O_CLOEXEC);
> + if (fdno < 0) {
> + rc = fdno;
> + goto out_fput;
> + }
> +
> @@ -332,6 +332,7 @@ union ucmd_buffer {
> struct iommu_ioas_unmap unmap;
> struct iommu_option option;
> struct iommu_vfio_ioas vfio_ioas;
> + struct iommu_fault_alloc fault;

alphabetic

> @@ -381,6 +382,8 @@ static const struct iommufd_ioctl_op
> iommufd_ioctl_ops[] = {
> val64),
> IOCTL_OP(IOMMU_VFIO_IOAS, iommufd_vfio_ioas, struct
> iommu_vfio_ioas,
> __reserved),
> + IOCTL_OP(IOMMU_FAULT_QUEUE_ALLOC, iommufd_fault_alloc,
> struct iommu_fault_alloc,
> + out_fault_fd),

ditto