[PATCH v4 14/23] iommufd: Add mmap interface

[Tian, Kevin]

> From: Nicolin Chen <nicolinc at nvidia.com>
> Sent: Friday, May 9, 2025 11:03 AM
> 
> +/*
> + * Kernel driver must first use the for-driver helpers to register an
> mmappable
> + * MMIO region to the iommufd core to allocate an offset. Then, it should
> report
> + * to user space this offset and the length of the MMIO region for mmap
> syscall,
> + * via a prior IOMMU_VIOMMU_ALLOC ioctl.
> + */

this comment better suits _iommufd_alloc_mmap()

> +static int iommufd_fops_mmap(struct file *filp, struct vm_area_struct *vma)
> +{
> +	struct iommufd_ctx *ictx = filp->private_data;
> +	size_t length = vma->vm_end - vma->vm_start;
> +	struct iommufd_mmap *immap;
> +	int rc;
> +
> +	if (!PAGE_ALIGNED(length))
> +		return -EINVAL;
> +	if (!(vma->vm_flags & VM_SHARED))
> +		return -EINVAL;
> +	if (vma->vm_flags & VM_EXEC)
> +		return -EPERM;
> +
> +	/* vma->vm_pgoff carries an index to an mtree entry (immap) */
> +	immap = mtree_load(&ictx->mt_mmap, vma->vm_pgoff);
> +	if (!immap)
> +		return -ENXIO;
> +	if (length >> PAGE_SHIFT != immap->num_pfns)
> +		return -ENXIO;
> +
> +	vma->vm_pgoff = 0;
> +	vma->vm_private_data = immap;
> +	vma->vm_ops = &iommufd_vma_ops;
> +	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> +	vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND |
> VM_DONTDUMP | VM_IO);
> +
> +	rc = remap_pfn_range(vma, vma->vm_start, immap->base_pfn,
> length,
> +			     vma->vm_page_prot);
> +	if (!rc) /* vm_ops.open won't be called for mmap itself. */
> +		refcount_inc(&immap->owner->users);
> +	return rc;

let's add some words for this refcnt thing in the commit msg.

Reviewed-by: Kevin Tian <kevin.tian at intel.com>