[PATCH v1 10/16] iommufd: Add mmap interface

Nicolin Chen
2025-04-11T06:38:40Z

For vIOMMU passing through HW resources to user space (VMs), add an mmap
infrastructure to map a region of hardware MMIO pages. The addr and size
should be given previously via a prior IOMMU_VIOMMU_ALLOC ioctl in some
output fields of the structure.

Maintain an mt_mmap per ictx for validations. And give IOMMU drivers a
pair of helpers to add and delete mmap regions onto the mt_mmap.

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
drivers/iommu/iommufd/iommufd_private.h | 9 ++++++
include/linux/iommufd.h | 15 ++++++++++
drivers/iommu/iommufd/driver.c | 40 +++++++++++++++++++++++++
drivers/iommu/iommufd/main.c | 35 ++++++++++++++++++++++
4 files changed, 99 insertions(+)

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index da35ffcc212b..5be0248966aa 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 +57,13 @@ 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;
+ bool is_io;
+};
+
/*
* 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 4118eaece1a5..e9394e20c4dd 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -226,6 +226,9 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
size_t size,
enum iommufd_object_type type);
void iommufd_object_abort(struct iommufd_ctx *ictx, struct iommufd_object *obj);
+int iommufd_ctx_alloc_mmap(struct iommufd_ctx *ictx, phys_addr_t base,
+ size_t size, bool is_io, 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,
@@ -246,6 +249,18 @@ static inline void iommufd_object_abort(struct iommufd_ctx *ictx,
{
}

+static inline int iommufd_ctx_alloc_mmap(struct iommufd_ctx *ictx,
+ phys_addr_t base, size_t size,
+ bool is_io, unsigned long *immap_id)
+{
+ return -EOPNOTSUPP;
+}
+
+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 7980a09761c2..abe0bdc1e9a3 100644
--- a/drivers/iommu/iommufd/driver.c
+++ b/drivers/iommu/iommufd/driver.c
@@ -50,6 +50,46 @@ void iommufd_object_abort(struct iommufd_ctx *ictx, struct iommufd_object *obj)
}
EXPORT_SYMBOL_NS_GPL(iommufd_object_abort, "IOMMUFD");

+/* Driver should report the immap_id to user space for mmap() syscalls */
+int iommufd_ctx_alloc_mmap(struct iommufd_ctx *ictx, phys_addr_t base,
+ size_t size, bool is_io, 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;
+ immap->is_io = is_io;
+
+ rc = mtree_alloc_range(&ictx->mt_mmap, immap_id, immap, sizeof(immap),
+ 0, LONG_MAX >> PAGE_SHIFT, GFP_KERNEL);
+ if (rc < 0) {
+ kfree(immap);
+ return rc;
+ }
+
+ /* mmap() syscall would 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 27473aff150f..d3101c76fcb8 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 +411,45 @@ static long iommufd_fops_ioctl(struct file *filp, unsigned int cmd,
return ret;
}

+/*
+ * The pfn and size carried in @vma from the user space mmap call should be
+ * previously given to user space via a prior ioctl output.
+ */
+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 of an mtree entry/immap */
+ immap = mtree_load(&ictx->mt_mmap, vma->vm_pgoff);
+ if (!immap)
+ return -EINVAL;
+ if (size >> PAGE_SHIFT > immap->pfn_end - immap->pfn_start + 1)
+ return -EINVAL;
+
+ vma->vm_pgoff = 0;
+ vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+ vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
+ if (immap->is_io)
+ vm_flags_set(vma, 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,
};

/**
--
2.43.0