Re: [PATCH v2 13/22] iommufd: Add mmap interface

Pranjal Shrivastava
2025-04-29T20:24:45Z

On Fri, Apr 25, 2025 at 10:58:08PM -0700, Nicolin Chen wrote:
> For vIOMMU passing through HW resources to user space (VMs), add an mmap
> infrastructure to map a region of hardware MMIO pages.
>
> Maintain an mt_mmap per ictx for validations. To allow IOMMU drivers to
> add and delete mmappable regions to/from the mt_mmap, add a pair of new
> helpers: iommufd_ctx_alloc_mmap() and iommufd_ctx_free_mmap().
>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
> drivers/iommu/iommufd/iommufd_private.h | 8 +++++
> include/linux/iommufd.h | 15 ++++++++++
> drivers/iommu/iommufd/driver.c | 39 +++++++++++++++++++++++++
> drivers/iommu/iommufd/main.c | 39 +++++++++++++++++++++++++
> 4 files changed, 101 insertions(+)
>
> diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
> index b974c207ae8a..db5b62ec4abb 100644
> --- a/drivers/iommu/iommufd/iommufd_private.h
> +++ b/drivers/iommu/iommufd/iommufd_private.h
> @@ -7,6 +7,7 @@
> #include <linux/iommu.h>
> #include <linux/iommufd.h>
> #include <linux/iova_bitmap.h>
> +#include <linux/maple_tree.h>
> #include <linux/rwsem.h>
> #include <linux/uaccess.h>
> #include <linux/xarray.h>
> @@ -44,6 +45,7 @@ struct iommufd_ctx {
> struct xarray groups;
> wait_queue_head_t destroy_wait;
> struct rw_semaphore ioas_creation_lock;
> + struct maple_tree mt_mmap;
>
> struct mutex sw_msi_lock;
> struct list_head sw_msi_list;
> @@ -55,6 +57,12 @@ struct iommufd_ctx {
> struct iommufd_ioas *vfio_ioas;
> };
>
> +/* Entry for iommufd_ctx::mt_mmap */
> +struct iommufd_mmap {
> + unsigned long pfn_start;
> + unsigned long pfn_end;
> +};
> +
> /*
> * The IOVA to PFN map. The map automatically copies the PFNs into multiple
> * domains and permits sharing of PFNs between io_pagetable instances. This
> diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
> index 5dff154e8ce1..d63e2d91be0d 100644
> --- a/include/linux/iommufd.h
> +++ b/include/linux/iommufd.h
> @@ -236,6 +236,9 @@ int iommufd_object_depend(struct iommufd_object *obj_dependent,
> struct iommufd_object *obj_depended);
> void iommufd_object_undepend(struct iommufd_object *obj_dependent,
> struct iommufd_object *obj_depended);
> +int iommufd_ctx_alloc_mmap(struct iommufd_ctx *ictx, phys_addr_t base,
> + size_t size, unsigned long *immap_id);
> +void iommufd_ctx_free_mmap(struct iommufd_ctx *ictx, unsigned long immap_id);
> struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu,
> unsigned long vdev_id);
> int iommufd_viommu_get_vdev_id(struct iommufd_viommu *viommu,
> @@ -262,11 +265,23 @@ static inline int iommufd_object_depend(struct iommufd_object *obj_dependent,
> return -EOPNOTSUPP;
> }
>
> +static inline int iommufd_ctx_alloc_mmap(struct iommufd_ctx *ictx,
> + phys_addr_t base, size_t size,
> + unsigned long *immap_id)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> static inline void iommufd_object_undepend(struct iommufd_object *obj_dependent,
> struct iommufd_object *obj_depended)
> {
> }
>
> +static inline void iommufd_ctx_free_mmap(struct iommufd_ctx *ictx,
> + unsigned long immap_id)
> +{
> +}
> +
> static inline struct device *
> iommufd_viommu_find_dev(struct iommufd_viommu *viommu, unsigned long vdev_id)
> {
> diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c
> index fb7f8fe40f95..c55336c580dc 100644
> --- a/drivers/iommu/iommufd/driver.c
> +++ b/drivers/iommu/iommufd/driver.c
> @@ -78,6 +78,45 @@ void iommufd_object_undepend(struct iommufd_object *obj_dependent,
> }
> EXPORT_SYMBOL_NS_GPL(iommufd_object_undepend, "IOMMUFD");
>
> +/* Driver should report the output @immap_id to user space for mmap() syscall */
> +int iommufd_ctx_alloc_mmap(struct iommufd_ctx *ictx, phys_addr_t base,
> + size_t size, unsigned long *immap_id)
> +{
> + struct iommufd_mmap *immap;
> + int rc;
> +
> + if (WARN_ON_ONCE(!immap_id))
> + return -EINVAL;
> + if (base & ~PAGE_MASK)
> + return -EINVAL;
> + if (!size || size & ~PAGE_MASK)
> + return -EINVAL;
> +
> + immap = kzalloc(sizeof(*immap), GFP_KERNEL);
> + if (!immap)
> + return -ENOMEM;
> + immap->pfn_start = base >> PAGE_SHIFT;
> + immap->pfn_end = immap->pfn_start + (size >> PAGE_SHIFT) - 1;
> +
> + rc = mtree_alloc_range(&ictx->mt_mmap, immap_id, immap, sizeof(immap),

I believe this should be sizeof(*immap) ?

> + 0, LONG_MAX >> PAGE_SHIFT, GFP_KERNEL);
> + if (rc < 0) {
> + kfree(immap);
> + return rc;
> + }
> +
> + /* mmap() syscall will right-shift the immap_id to vma->vm_pgoff */
> + *immap_id <<= PAGE_SHIFT;
> + return 0;
> +}
> +EXPORT_SYMBOL_NS_GPL(iommufd_ctx_alloc_mmap, "IOMMUFD");
> +
> +void iommufd_ctx_free_mmap(struct iommufd_ctx *ictx, unsigned long immap_id)
> +{
> + kfree(mtree_erase(&ictx->mt_mmap, immap_id >> PAGE_SHIFT));
> +}
> +EXPORT_SYMBOL_NS_GPL(iommufd_ctx_free_mmap, "IOMMUFD");
> +
> /* Caller should xa_lock(&viommu->vdevs) to protect the return value */
> struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu,
> unsigned long vdev_id)
> diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
> index ac51d5cfaa61..4b46ea47164d 100644
> --- a/drivers/iommu/iommufd/main.c
> +++ b/drivers/iommu/iommufd/main.c
> @@ -213,6 +213,7 @@ static int iommufd_fops_open(struct inode *inode, struct file *filp)
> xa_init_flags(&ictx->objects, XA_FLAGS_ALLOC1 | XA_FLAGS_ACCOUNT);
> xa_init(&ictx->groups);
> ictx->file = filp;
> + mt_init_flags(&ictx->mt_mmap, MT_FLAGS_ALLOC_RANGE);
> init_waitqueue_head(&ictx->destroy_wait);
> mutex_init(&ictx->sw_msi_lock);
> INIT_LIST_HEAD(&ictx->sw_msi_list);
> @@ -410,11 +411,49 @@ static long iommufd_fops_ioctl(struct file *filp, unsigned int cmd,
> return ret;
> }
>
> +/*
> + * Kernel driver must first do iommufd_ctx_alloc_mmap() to register an mmappable
> + * MMIO region to the iommufd core to receive an "immap_id". Then, driver should
> + * report to user space this immap_id and the size of the registered MMIO region
> + * for @vm_pgoff and @size of an mmap() call, via an IOMMU_VIOMMU_ALLOC ioctl in
> + * the output fields of its driver-type data structure.
> + *
> + * Note the @size is allowed to be smaller than the registered size as a partial
> + * mmap starting from the registered base address.
> + */
> +static int iommufd_fops_mmap(struct file *filp, struct vm_area_struct *vma)
> +{
> + struct iommufd_ctx *ictx = filp->private_data;
> + size_t size = vma->vm_end - vma->vm_start;
> + struct iommufd_mmap *immap;
> +
> + if (size & ~PAGE_MASK)
> + return -EINVAL;
> + if (!(vma->vm_flags & VM_SHARED))
> + return -EINVAL;
> + if (vma->vm_flags & VM_EXEC)
> + return -EPERM;
> +
> + /* vm_pgoff carries an index (immap_id) to an mtree entry (immap) */
> + immap = mtree_load(&ictx->mt_mmap, vma->vm_pgoff);
> + if (!immap)
> + return -ENXIO;
> + if (size >> PAGE_SHIFT > immap->pfn_end - immap->pfn_start + 1)
> + return -ENXIO;
> +
> + vma->vm_pgoff = 0;
> + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> + vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_IO);
> + return remap_pfn_range(vma, vma->vm_start, immap->pfn_start, size,
> + vma->vm_page_prot);
> +}
> +
> static const struct file_operations iommufd_fops = {
> .owner = THIS_MODULE,
> .open = iommufd_fops_open,
> .release = iommufd_fops_release,
> .unlocked_ioctl = iommufd_fops_ioctl,
> + .mmap = iommufd_fops_mmap,
> };
>
> /**

Thanks,
Praan

> --
> 2.43.0
>