vfio: selftests: igb: Add driver for Intel 82576 device

Add a VFIO selftest driver for the Intel Gigabit Ethernet controller
(IGB), specifically targeting the 82576 device. IGB is fully virtualized

vfio: selftests: igb: Add driver for Intel 82576 device

Add a VFIO selftest driver for the Intel Gigabit Ethernet controller
(IGB), specifically targeting the 82576 device. IGB is fully virtualized
in QEMU which makes it easy to run VFIO selftests without needing any
specific hardware.

Since IGB is an Ethernet device, it cannot support DMA transfers smaller
than the minimum Ethernet payload size (60 bytes) without hardware padding
corrupting adjacent memory. The driver asserts that the transfer size is
at least 60 bytes to prevent this.

All VFIO selftest drivers must implement DMA/memcpy operations, but IGB
doesn't have a native memcpy feature, so the loopback feature (described
in section 3.5.6.3 of IGB specification) is used to implement it. To
support testing on both QEMU and physical hardware, the driver uses PHY
internal loopback with some QEMU-specific fallbacks. The driver also
supports MSI-X routing and interrupt management, and disables PCIe
completion timeout retries to ensure clean recovery during invalid-DMA
tests.

Users can verify the driver works in QEMU by building the kernel,
building VFIO selftests, and then running the vfio_pci_driver_test using
this command:

vng \
--run arch/x86/boot/bzImage \
--user root \
--disable-microvm \
--memory 32G \
--cpus 8 \
--qemu-opts="-M q35,accel=kvm,kernel-irqchip=split" \
--qemu-opts="-device intel-iommu,intremap=on,caching-mode=on,device-iotlb=on" \
--qemu-opts="-netdev user,id=net0 -device igb,netdev=net0,addr=09.0" \
--append "console=ttyS0 earlyprintk=ttyS0 intel_iommu=on iommu=pt" \
--exec "modprobe vfio-pci && \
./tools/testing/selftests/vfio/scripts/setup.sh 0000:00:09.0 && \
./tools/testing/selftests/vfio/scripts/run.sh ./tools/testing/selftests/vfio/vfio_pci_driver_test"

Assisted-by: Claude:claude-opus-4-7
Assisted-by: Gemini:gemini-3.1-pro-preview
Co-developed-by: Alex Williamson <alex.williamson@nvidia.com>
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
Signed-off-by: Josh Hilke <jrhilke@google.com>
Acked-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20260805-igb_v3_b4-v10-2-9c86dc849c0d@google.com
Signed-off-by: Alex Williamson <alex@shazbot.org>

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