[PATCH 0/2] vfio/pci: Request resources and map BARs at enable time

[Matt Evans <mattev@meta.com>]

Hi,

This is a replacement for these patches posted to set up the
VFIO barmap in the DMABUF export path, and add serialisation:

 https://lore.kernel.org/kvm/20260415181423.1008458-1-mattev@meta.com

Those patches were motivated by the DMABUF export originally missing a
call to vfio_pci_core_setup_barmap() and so possibly exporting a range
for which resources weren't yet requested.

Responses in the thread indicated there wasn't a strong historical
reason to require the bar-mapping to be performed on-demand at BAR
reference time.  It's much simpler to move this to
vfio_pci_core_enable(), and that then avoids having to deal with
concurrent lazy requests.

Now VFIO drivers requiring the BAR resources (mmap(), DMABUF export,
etc.) don't need to do anything else, and there's nothing to forget in
future code.

The first patch sets up the barmap (requesting PCI resources and
ioremap() of the BARs) in vfio_pci_core_enable().  It can be
considered a bugfix for the VFIO DMABUF path.

The second patch removes calls to vfio_pci_core_setup_barmap(), which
were left untouched but harmless (just a stub) in the first patch.

However, vfio_pci_core_setup_barmap() did two things, requesting
resources and ioremap()ing them.  Some callers relied on it to perform
the ioremap() just before an in-kernel access to the BAR (e.g. the BAR
R/W routines, nvgrace-gpu).  These calls are replaced by a cheap check
that the required BAR has indeed been mapped, keeping the same
behaviour.

In future we could reconsider performing all the ioremap()s at startup
time, since a lot of VFIO users will never access BARs in-kernel and
won't need them.  Mapping huge BARs will cost some time & memory, and
if necessary this could be reduced by doing the ioremap() portion on
demand.


Matt Evans (2):
  vfio/pci: Set up barmap in vfio_pci_core_enable()
  vfio/pci: Remove vfio_pci_core_setup_barmap()

 drivers/vfio/pci/nvgrace-gpu/main.c | 11 ++---
 drivers/vfio/pci/vfio_pci_core.c    | 71 ++++++++++++++++++++++-------
 drivers/vfio/pci/vfio_pci_rdwr.c    | 35 ++------------
 drivers/vfio/pci/virtio/legacy_io.c |  5 +-
 4 files changed, 65 insertions(+), 57 deletions(-)

-- 
2.47.3