[PATCH v4 0/3] vfio/pci: Introduce vfio_pci driver for ISM devices

Julian Ruess
2026-03-13T14:40:48Z

Hi all,

This series adds a vfio_pci variant driver for the s390-specific
Internal Shared Memory (ISM) devices used for inter-VM communication
including SMC-D.

This is a prerequisite for an in-development open-source user space
driver stack that will allow to use ISM devices to provide remote
console and block device functionality. This stack will be part of
s390-tools.

This driver would also allow QEMU to mediate access to an ISM device,
enabling a form of PCI pass-through even for guests whose hardware
cannot directly execute PCI accesses, such as nested guests.

On s390, kernel primitives such as ioread() and iowrite() are switched
over from function handle based PCI load/stores instructions to PCI
memory-I/O (MIO) loads/stores when these are available and not
explicitly disabled. Since these instructions cannot be used with ISM
devices, ensure that classic function handle-based PCI instructions are
used instead.

The driver is still required even when MIO instructions are disabled, as
the ISM device relies on the PCI store‑block (PCISTB) instruction to
perform write operations.

Thank you,
Julian

Signed-off-by: Julian Ruess <julianr@linux.ibm.com>
---
Changes in v4:
- Fix bug with < 8 byte reads. For code simplicity, only support 8 byte reads.
- Fix leak of ivpcd.
- Fix cache replacement by implementing a per-device kmem_cache.
- Link to v3: https://lore.kernel.org/r/20260305-vfio_pci_ism-v3-0-1217076c81d9@linux.ibm.com

Changes in v3:
- Add comments to ism_vfio_pci_do_io_r() and ism_vfio_pci_do_io_w().
- Format Kconfig.
- Add 4k boundary check to ism_vfio_pci_do_io_w().
- Use kmem_cache instead of kzalloc in ism_vfio_pci_do_io_w().
- Add error handler to struct ism_vfio_pci_driver.
- Link to v2: https://lore.kernel.org/r/20260224-vfio_pci_ism-v2-0-f010945373fa@linux.ibm.com

Changes in v2:
- Remove common code patch that sets VFIO_PCI_OFFSET_SHIFT to 48.
- Implement ism_vfio_pci_ioctl_get_region_info() to have own region
offsets.
- For config space accesses, rename vfio_config_do_rw() to
vfio_pci_config_rw_single() and export it.
- Use zdev->maxstbl instead of ZPCI_BOUNDARY_SIZE.
- Add comment that zPCI must not use MIO instructions for config space
access.
- Rework patch descriptions.
- Update license info.
- Link to v1: https://lore.kernel.org/r/20260212-vfio_pci_ism-v1-0-333262ade074@linux.ibm.com

---
Julian Ruess (3):
vfio/pci: Rename vfio_config_do_rw() to vfio_pci_config_rw_single() and export it
vfio/ism: Implement vfio_pci driver for ISM devices
MAINTAINERS: add VFIO ISM PCI DRIVER section

MAINTAINERS | 6 +
drivers/vfio/pci/Kconfig | 2 +
drivers/vfio/pci/Makefile | 2 +
drivers/vfio/pci/ism/Kconfig | 10 ++
drivers/vfio/pci/ism/Makefile | 3 +
drivers/vfio/pci/ism/main.c | 345 +++++++++++++++++++++++++++++++++++++
drivers/vfio/pci/vfio_pci_config.c | 8 +-
drivers/vfio/pci/vfio_pci_priv.h | 4 +
8 files changed, 377 insertions(+), 3 deletions(-)
---
base-commit: 0257f64bdac7fdca30fa3cae0df8b9ecbec7733a
change-id: 20250227-vfio_pci_ism-0ccc2e472247

Best regards,
--
Julian Ruess <julianr@linux.ibm.com>