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

From: Nicolin Chen nicolinc@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@intel.com