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

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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@xxxxxxxxxxxxx/

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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