[PATCH V4 04/10] iommufd: Add an ioctl IOMMU_IOAS_GET_PA to query PA from IOVA

Jacob Pan
2026-04-14T21:14:17Z

To support no-IOMMU mode where userspace drivers perform unsafe DMA
using physical addresses, introduce a new API to retrieve the
physical address of a user-allocated DMA buffer that has been mapped to
an IOVA via IOAS. The mapping is backed by mock I/O page tables maintained
by generic IOMMUPT framework.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Jacob Pan <jacob.pan@linux.microsoft.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
v4:
- Fix unaligned IOVA length (Sashiko)
v2:
- Scan the contiguous physical-address span beyond the first page and return its length.
---
drivers/iommu/iommufd/io_pagetable.c | 60 +++++++++++++++++++++++++
drivers/iommu/iommufd/ioas.c | 25 +++++++++++
drivers/iommu/iommufd/iommufd_private.h | 3 ++
drivers/iommu/iommufd/main.c | 3 ++
include/uapi/linux/iommufd.h | 25 +++++++++++
5 files changed, 116 insertions(+)

diff --git a/drivers/iommu/iommufd/io_pagetable.c b/drivers/iommu/iommufd/io_pagetable.c
index ee003bb2f647..04336a8e12f5 100644
--- a/drivers/iommu/iommufd/io_pagetable.c
+++ b/drivers/iommu/iommufd/io_pagetable.c
@@ -849,6 +849,66 @@ int iopt_unmap_iova(struct io_pagetable *iopt, unsigned long iova,
return iopt_unmap_iova_range(iopt, iova, iova_last, unmapped);
}

+int iopt_get_phys(struct io_pagetable *iopt, unsigned long iova, u64 *paddr,
+ u64 *length)
+{
+ struct iopt_area *area;
+ u64 tmp_length = 0;
+ u64 tmp_paddr = 0;
+ int rc = 0;
+
+ if (!IS_ENABLED(CONFIG_VFIO_NOIOMMU))
+ return -EOPNOTSUPP;
+
+ down_read(&iopt->iova_rwsem);
+ area = iopt_area_iter_first(iopt, iova, iova);
+ if (!area || !area->pages) {
+ rc = -ENOENT;
+ goto unlock_exit;
+ }
+
+ if (!area->storage_domain ||
+ area->storage_domain->owner != &iommufd_noiommu_ops) {
+ rc = -EOPNOTSUPP;
+ goto unlock_exit;
+ }
+
+ *paddr = iommu_iova_to_phys(area->storage_domain, iova);
+ if (!*paddr) {
+ rc = -EINVAL;
+ goto unlock_exit;
+ }
+
+ tmp_length = PAGE_SIZE - offset_in_page(iova);
+ tmp_paddr = *paddr;
+ /*
+ * Scan the domain for the contiguous physical address length so that
+ * userspace search can be optimized for fewer ioctls.
+ */
+ while (iova < iopt_area_last_iova(area)) {
+ unsigned long next_iova;
+ u64 next_paddr;
+
+ if (check_add_overflow(iova, PAGE_SIZE, &next_iova))
+ break;
+
+ next_paddr = iommu_iova_to_phys(area->storage_domain, next_iova);
+
+ if (!next_paddr || next_paddr != tmp_paddr + PAGE_SIZE)
+ break;
+
+ iova = next_iova;
+ tmp_paddr += PAGE_SIZE;
+ tmp_length += PAGE_SIZE;
+ }
+ *length = tmp_length;
+
+unlock_exit:
+ up_read(&iopt->iova_rwsem);
+
+ return rc;
+}
+
int iopt_unmap_all(struct io_pagetable *iopt, unsigned long *unmapped)
{
/* If the IOVAs are empty then unmap all succeeds */
diff --git a/drivers/iommu/iommufd/ioas.c b/drivers/iommu/iommufd/ioas.c
index fed06c2b728e..93cebb4c23bd 100644
--- a/drivers/iommu/iommufd/ioas.c
+++ b/drivers/iommu/iommufd/ioas.c
@@ -375,6 +375,31 @@ int iommufd_ioas_unmap(struct iommufd_ucmd *ucmd)
return rc;
}

+int iommufd_ioas_get_pa(struct iommufd_ucmd *ucmd)
+{
+ struct iommu_ioas_get_pa *cmd = ucmd->cmd;
+ struct iommufd_ioas *ioas;
+ int rc;
+
+ if (cmd->flags || cmd->__reserved)
+ return -EOPNOTSUPP;
+
+ ioas = iommufd_get_ioas(ucmd->ictx, cmd->ioas_id);
+ if (IS_ERR(ioas))
+ return PTR_ERR(ioas);
+
+ rc = iopt_get_phys(&ioas->iopt, cmd->iova, &cmd->out_phys,
+ &cmd->out_length);
+ if (rc)
+ goto out_put;
+
+ rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
+out_put:
+ iommufd_put_object(ucmd->ictx, &ioas->obj);
+
+ return rc;
+}
+
static void iommufd_release_all_iova_rwsem(struct iommufd_ctx *ictx,
struct xarray *ioas_list)
{
diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 2682b5baa6e9..0e772882aee9 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -118,6 +118,8 @@ int iopt_map_pages(struct io_pagetable *iopt, struct list_head *pages_list,
int iopt_unmap_iova(struct io_pagetable *iopt, unsigned long iova,
unsigned long length, unsigned long *unmapped);
int iopt_unmap_all(struct io_pagetable *iopt, unsigned long *unmapped);
+int iopt_get_phys(struct io_pagetable *iopt, unsigned long iova, u64 *paddr,
+ u64 *length);

int iopt_read_and_clear_dirty_data(struct io_pagetable *iopt,
struct iommu_domain *domain,
@@ -346,6 +348,7 @@ int iommufd_ioas_map_file(struct iommufd_ucmd *ucmd);
int iommufd_ioas_change_process(struct iommufd_ucmd *ucmd);
int iommufd_ioas_copy(struct iommufd_ucmd *ucmd);
int iommufd_ioas_unmap(struct iommufd_ucmd *ucmd);
+int iommufd_ioas_get_pa(struct iommufd_ucmd *ucmd);
int iommufd_ioas_option(struct iommufd_ucmd *ucmd);
int iommufd_option_rlimit_mode(struct iommu_option *cmd,
struct iommufd_ctx *ictx);
diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 8c6d43601afb..ebae01ed947d 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -432,6 +432,7 @@ union ucmd_buffer {
struct iommu_veventq_alloc veventq;
struct iommu_vfio_ioas vfio_ioas;
struct iommu_viommu_alloc viommu;
+ struct iommu_ioas_get_pa get_pa;
#ifdef CONFIG_IOMMUFD_TEST
struct iommu_test_cmd test;
#endif
@@ -484,6 +485,8 @@ static const struct iommufd_ioctl_op iommufd_ioctl_ops[] = {
struct iommu_ioas_map_file, iova),
IOCTL_OP(IOMMU_IOAS_UNMAP, iommufd_ioas_unmap, struct iommu_ioas_unmap,
length),
+ IOCTL_OP(IOMMU_IOAS_GET_PA, iommufd_ioas_get_pa, struct iommu_ioas_get_pa,
+ out_phys),
IOCTL_OP(IOMMU_OPTION, iommufd_option, struct iommu_option, val64),
IOCTL_OP(IOMMU_VDEVICE_ALLOC, iommufd_vdevice_alloc_ioctl,
struct iommu_vdevice_alloc, virt_id),
diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
index 1dafbc552d37..9afe0a1b11a0 100644
--- a/include/uapi/linux/iommufd.h
+++ b/include/uapi/linux/iommufd.h
@@ -57,6 +57,7 @@ enum {
IOMMUFD_CMD_IOAS_CHANGE_PROCESS = 0x92,
IOMMUFD_CMD_VEVENTQ_ALLOC = 0x93,
IOMMUFD_CMD_HW_QUEUE_ALLOC = 0x94,
+ IOMMUFD_CMD_IOAS_GET_PA = 0x95,
};

/**
@@ -219,6 +220,30 @@ struct iommu_ioas_map {
};
#define IOMMU_IOAS_MAP _IO(IOMMUFD_TYPE, IOMMUFD_CMD_IOAS_MAP)

+/**
+ * struct iommu_ioas_get_pa - ioctl(IOMMU_IOAS_GET_PA)
+ * @size: sizeof(struct iommu_ioas_get_pa)
+ * @flags: Reserved, must be 0 for now
+ * @ioas_id: IOAS ID to query IOVA to PA mapping from
+ * @__reserved: Must be 0
+ * @iova: IOVA to query
+ * @out_length: Number of bytes contiguous physical address starting from phys
+ * @out_phys: Output physical address the IOVA maps to
+ *
+ * Query the physical address backing an IOVA range. The entire range must be
+ * mapped already. For noiommu devices doing unsafe DMA only.
+ */
+struct iommu_ioas_get_pa {
+ __u32 size;
+ __u32 flags;
+ __u32 ioas_id;
+ __u32 __reserved;
+ __aligned_u64 iova;
+ __aligned_u64 out_length;
+ __aligned_u64 out_phys;
+};
+#define IOMMU_IOAS_GET_PA _IO(IOMMUFD_TYPE, IOMMUFD_CMD_IOAS_GET_PA)
+
/**
* struct iommu_ioas_map_file - ioctl(IOMMU_IOAS_MAP_FILE)
* @size: sizeof(struct iommu_ioas_map_file)
--
2.34.1