[PATCH v3 0/3] vfio/pci: Support 8-byte PCI loads and stores

Gerd Bayer
2024-04-25T16:56:16Z

Hi all,

this all started with a single patch by Ben to enable writing a user-mode
driver for a PCI device that requires 64bit register read/writes on s390.
A quick grep showed that there are several other drivers for PCI devices
in the kernel that use readq/writeq and eventually could use this, too.
So we decided to propose this for general inclusion.

A couple of suggestions for refactorizations by Jason Gunthorpe and Alex
Williamson later [1], I arrived at this little series that avoids some
code duplication and structures the different-size accesses in
vfio_pci_core_do_io_rw() in a way that the conditional compile of
8-byte accesses no longer creates an odd split of "else-if".

The initial version was tested with a PCI device on s390. This version
has only been tested for reads of 1..8 byte sizes and only been compile
tested for a 32bit architecture (arm).

Thank you,
Gerd Bayer

[1] https://lore.kernel.org/all/20240422153508.2355844-1-gbayer@linux.ibm.com/

Changes v2 -> v3:
- Introduce macro to generate body of different-size accesses in
vfio_pci_core_do_io_rw (courtesy Alex Williamson).
- Convert if-else if chain to a switch-case construct to better
accommodate conditional compiles.

Changes v1 -> v2:
- On non 64bit architecture use at most 32bit accesses in
vfio_pci_core_do_io_rw and describe that in the commit message.
- Drop the run-time error on 32bit architectures.
- The #endif splitting the "else if" is not really fortunate, but I'm
open to suggestions.

Ben Segal (1):
vfio/pci: Support 8-byte PCI loads and stores

Gerd Bayer (2):
vfio/pci: Extract duplicated code into macro
vfio/pci: Continue to refactor vfio_pci_core_do_io_rw

drivers/vfio/pci/vfio_pci_rdwr.c | 154 +++++++++++++++++--------------
include/linux/vfio_pci_core.h | 3 +
2 files changed, 90 insertions(+), 67 deletions(-)

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2.44.0