Re: [PATCH v6 00/18] Support VFIO cdev API in DPDK

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 21 Nov 2025 10:08:45 +0000
Anatoly Burakov <anatoly.burakov@intel.com> wrote:

> This patchset introduces a major refactor of the VFIO subsystem in DPDK to
> support character device (cdev) interface introduced in Linux kernel, as well as
> make the API more streamlined and useful. The goal is to simplify device
> management, improve compatibility, and clarify API responsibilities.
> 
> The following sections outline the key issues addressed by this patchset and the
> corresponding changes introduced.
> 
> 1. Only group mode is supported
> ===============================
> 
> Since kernel version 4.14.327 (LTS), VFIO supports the new character device
> (cdev)-based way of working with VFIO devices (otherwise known as IOMMUFD). This
> is a device-centric mode and does away with all the complexity regarding groups
> and IOMMU types, delegating it all to the kernel, and exposes a much simpler
> interface to userspace.
> 
> The old group interface is still around, and will need to be kept in DPDK both
> for compatibility reasons, as well as supporting special cases (FSLMC bus, NBL
> driver, etc.).
> 
> To enable this, VFIO is heavily refactored, so that the code can support both
> modes while relying on (mostly) common infrastructure.
> 
> Note that the existing `rte_vfio_device_setup/release` model is fundamentally
> incompatible with cdev mode, because for custom container cases, the expected
> flow is that the user binds the IOMMU group (and thus, implicitly, the device
> itself) to a specific container using `rte_vfio_container_group_bind`, whereas
> this step is not needed for cdev as the device fd is assigned to the container
> straight away.
> 
> Therefore, what we do instead is introduce a new API for container device
> assignment which, semantically, will assign a device to specified container, so
> that when it is mapped using `rte_pci_map_device`, the appropriate container is
> selected. Under the hood though, we essentially transition to getting device fd
> straight away at assign stage, so that by the time the PCI bus attempts to map
> the device, it is already mapped and we just return an fd. There is no
> "unassign" API because `release_device` already performs that function.
> 
> Additionally, a new `rte_vfio_get_mode` API is added for those cases that need
> some introspection into VFIO's internals, with three new modes: group
> (old-style), no-iommu (old-style but without IOMMU), and cdev (the new mode).
> Although no-IOMMU is technically a variant of group mode, the distinction is
> largely irrelevant to the user, as all usages of noiommu checks in our codebase
> are for deciding whether to use IOVA or PA, not anything to do with managing
> groups. The current plan for kernel community is to *not* introduce no-IOMMU
> cdev implementation, which is why this will be kept for compatibility for these
> use cases.
> 
> There were other users of VFIO which relied on group API but only for convenience
> purposes; no actual VFIO functionality depended on those API's. Therefore, group
> API's are removed and, where appropriate, replaced with the new API's.
> 
> List of removed API's:
> 
> * `rte_vfio_get_group_fd`
> * `rte_vfio_clear_group`
> * `rte_vfio_container_group_bind` (replaced by container assign API)
> * `rte_vfio_container_group_unbind`
> * `rte_vfio_noiommu_is_enabled` (replaced by new mode API)
> 
> 2. The API responsibilities aren't clear and bleed into each other
> ==================================================================
> 
> Some API's do multiple things at once. In particular:
> 
> * `rte_vfio_get_device_info` will setup the device
> * `rte_vfio_setup_device` will get device info
> 
> These API's have been adjusted to do one thing only.
> 
> v6:
> - Fixed missing header include in vfio cdev file
> 
> v5:
> - Added back missing uapi patch
> 
> v4:
> - Fixed issues with documenting rte_vfio_mode enum
> - Separated deprecation notices into a separate patchset
> 
> v3:
> - Make API removal cleaner
> - Fix `get_group_num` usages to align with new API
> - Fix issues with function exports
> - Fix issues with `setup_device` returning old-style values in some cases
> 
> v2:
> - Make the entire API internal
> - More aggressive API pruning, complete removal of group API
> - Fixed a bug in group mode where device could not be used
> - Better documentation and deprecation notice patches
> - Moved doc patches to beginning of patchset
> 
> Anatoly Burakov (18):
>   uapi: update to v6.17 and add iommufd.h
>   vfio: make all functions internal
>   vfio: split get device info from setup
>   vfio: add container device assignment API
>   net/nbl: do not use VFIO group bind API
>   net/ntnic: use container device assignment API
>   vdpa/ifc: use container device assignment API
>   vdpa/nfp: use container device assignment API
>   vdpa/sfc: use container device assignment API
>   vhost: remove group-related API from drivers
>   vfio: remove group-based API
>   vfio: cleanup and refactor
>   bus/pci: use the new VFIO mode API
>   bus/fslmc: use the new VFIO mode API
>   net/hinic3: use the new VFIO mode API
>   net/ntnic: use the new VFIO mode API
>   vfio: remove no-IOMMU check API
>   vfio: introduce cdev mode
> 
>  config/arm/meson.build                    |    1 +
>  config/meson.build                        |    1 +
>  doc/guides/prog_guide/vhost_lib.rst       |    4 -
>  drivers/bus/cdx/cdx_vfio.c                |   25 +-
>  drivers/bus/fslmc/fslmc_bus.c             |   10 +-
>  drivers/bus/fslmc/fslmc_vfio.c            |    6 +-
>  drivers/bus/pci/linux/pci.c               |    2 +-
>  drivers/bus/pci/linux/pci_vfio.c          |   33 +-
>  drivers/bus/platform/platform.c           |    9 +-
>  drivers/crypto/bcmfs/bcmfs_vfio.c         |   14 +-
>  drivers/net/hinic3/base/hinic3_hwdev.c    |    2 +-
>  drivers/net/nbl/nbl_common/nbl_userdev.c  |   20 +-
>  drivers/net/nbl/nbl_include/nbl_include.h |    1 +
>  drivers/net/ntnic/ntnic_ethdev.c          |    2 +-
>  drivers/net/ntnic/ntnic_vfio.c            |   30 +-
>  drivers/vdpa/ifc/ifcvf_vdpa.c             |   34 +-
>  drivers/vdpa/mlx5/mlx5_vdpa.c             |    1 -
>  drivers/vdpa/nfp/nfp_vdpa.c               |   37 +-
>  drivers/vdpa/sfc/sfc_vdpa.c               |   39 +-
>  drivers/vdpa/sfc/sfc_vdpa.h               |    2 -
>  kernel/linux/uapi/linux/iommufd.h         | 1292 +++++++++++
>  kernel/linux/uapi/linux/vduse.h           |    2 +-
>  kernel/linux/uapi/linux/vfio.h            |   12 +-
>  kernel/linux/uapi/version                 |    2 +-
>  lib/eal/freebsd/eal.c                     |   98 +-
>  lib/eal/include/rte_vfio.h                |  387 ++--
>  lib/eal/linux/eal_vfio.c                  | 2433 ++++++++-------------
>  lib/eal/linux/eal_vfio.h                  |  167 +-
>  lib/eal/linux/eal_vfio_cdev.c             |  390 ++++
>  lib/eal/linux/eal_vfio_group.c            |  984 +++++++++
>  lib/eal/linux/eal_vfio_mp_sync.c          |   80 +-
>  lib/eal/linux/meson.build                 |    2 +
>  lib/eal/windows/eal.c                     |    4 +-
>  lib/vhost/vdpa_driver.h                   |    3 -
>  34 files changed, 4261 insertions(+), 1868 deletions(-)
>  create mode 100644 kernel/linux/uapi/linux/iommufd.h
>  create mode 100644 lib/eal/linux/eal_vfio_cdev.c
>  create mode 100644 lib/eal/linux/eal_vfio_group.c
> 

Since this is a big patch and hard to see everything, ran the patch
series through AI with the current AGENTS.md guideline.
Agree that a release note is needed.


## DPDK Patch Review: VFIO cdev Mode Series (v6, 18 patches)

**Author:** Anatoly Burakov <anatoly.burakov@intel.com>

### Overview
This 18-patch series introduces VFIO cdev (IOMMUFD) mode support, refactors VFIO infrastructure, and makes VFIO APIs internal. The series is at v6 and has accumulated several Acked-by tags.

---

### ✅ PASSED Checks

| Check | Status |
|-------|--------|
| Subject lines ≤60 characters | ✓ All pass |
| Subject lowercase (except acronyms) | ✓ Correct |
| Component prefixes | ✓ Valid: `vfio:`, `bus/pci:`, `net/nbl:`, `vdpa/sfc:`, etc. |
| No trailing periods in subjects | ✓ None found |
| Body wrapped at 75 characters | ✓ All pass |
| Body does not start with "It" | ✓ Confirmed |
| `Signed-off-by:` present | ✓ All 18 patches |
| VF/PF capitalization | ✓ Correct usage |
| SPDX license in new files | ✓ BSD-3-Clause with copyright in `eal_vfio_group.c`, `eal_vfio_cdev.c` |
| `__rte_internal` placement | ✓ Alone on line, in header files only |
| Kernel UAPI headers | ✓ GPL-2.0 (appropriate for kernel headers) |
| Tag order | ✓ Correct (Signed-off-by before Acked-by) |

---

### ⚠️ WARNINGS (should fix)

#### 1. Missing Release Notes
**Severity:** Warning  
**Location:** Series-wide

This series makes significant API changes that warrant release notes:

- **Patch 02/18:** Makes entire VFIO API internal-only (ABI change for applications)
- **Patch 12/18:** Changes return value semantics for `rte_vfio_setup_device()` and `rte_vfio_get_group_num()` (now return -1 with `rte_errno=ENODEV` instead of 1)
- **Patch 18/18:** Introduces new VFIO cdev mode (`RTE_VFIO_MODE_CDEV`)

**Recommendation:** Add entry to `doc/guides/rel_notes/release_25_XX.rst` documenting:
- VFIO API is now internal (drivers only)
- Return value changes for affected functions
- New cdev/IOMMUFD mode support

#### 2. Implicit Integer Comparison
**Severity:** Warning  
**Location:** Patch 12/18, `eal_vfio_group.c`

```c
// Line ~8360 in mbox (in vfio_has_supported_extensions function)
if (!n_extensions)    // n_extensions is unsigned int
```

**Should be:**
```c
if (n_extensions == 0)
```

Per AGENTS.md: "Integers - compare explicitly with zero"

---

### ℹ️ INFO (observations)

1. **Good commit message structure:** The series has well-written commit messages, particularly patch 12/18 which clearly documents the behavioral changes.

2. **Proper API tagging:** All new internal APIs use `__rte_internal` correctly positioned.

3. **Kernel header long line:** Line 613 in `iommufd.h` exceeds 100 chars, but this is a verbatim kernel UAPI header import - acceptable.

4. **Acks accumulated:** Patches 01, 12, and 14 have maintainer Acks (Stephen Hemminger, Hemant Agrawal).

---

### Summary

| Category | Count |
|----------|-------|
| Errors | 0 |
| Warnings | 2 |
| Info | 4 |

**Verdict:** The series is in good shape for this stage (v6). The two warnings should be addressed before merging:
1. Add release notes for the API changes
2. Fix the implicit integer comparison in `vfio_has_supported_extensions()`