Leander Kohler b67e7da10c pci: Detect masked BAR size probes ...

A PCI BAR stores its address in the upper bits and type information in
the lower bits. To determine the BAR size, an operating system disables
memory decoding, writes ones to the BAR's address bits, and reads the
value back. Bits that remain zero reveal the required alignment and
therefore the size.

We currently recognize only 0xffffffff as a size probe. OpenBSD instead
writes the memory BAR address mask 0xfffffff0, without setting the lower
four non-address bits [0][1].

We misinterpret that probe as a real BAR relocation. Because OpenBSD has
disabled memory space, the relocation remains pending. We apply it when
OpenBSD enables memory space again, moving the virtio block BAR away
from its mapped address and preventing the guest from booting.

Recognize probes using the address mask for each BAR type and exclude
them from BAR reprogramming. Add a test for the OpenBSD memory BAR
probe.

[0]: 54a2bc1e54/sys/dev/pci/pci_map.c (L154-L180)
[1]: 54a2bc1e54/sys/dev/pci/pcireg.h (L429-L443)

Co-authored-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>
On-behalf-of: SAP leander.kohler@sap.com
Signed-off-by: Leander Kohler <leander.kohler@cyberus-technology.de>

2026-07-17 11:58:32 +00:00

..

src

pci: Detect masked BAR size probes

2026-07-17 11:58:32 +00:00

Cargo.toml

pci: vfio: Implement save path state transitions

2026-07-02 01:13:03 +00:00