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vfio/igd: add new bar0 quirk to emulate BDSM mirror

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The BDSM register is mirrored into MMIO space at least for gen 11 and
later devices. Unfortunately, the Windows driver reads the register
value from MMIO space instead of PCI config space for those devices [1].
Therefore, we either have to keep a 1:1 mapping for the host and guest
address or we have to emulate the MMIO register too. Using the igd in
legacy mode is already hard due to it's many constraints. Keeping a 1:1
mapping may not work in all cases and makes it even harder to use. An
MMIO emulation has to trap the whole MMIO page. This makes accesses to
this page slower compared to using second level address translation.
Nevertheless, it doesn't have any constraints and I haven't noticed any
performance degradation yet making it a better solution.

[1] 5c351bee0f/devicemodel/hw/pci/passthrough.c (L650-L653)

Signed-off-by: Corvin Köhne <c.koehne@beckhoff.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
This commit is contained in:
Corvin Köhne 2024-08-28 15:43:25 +02:00 • committed by Cédric Le Goater
parent 7bafcd1767
commit 11b5ce95be
3 changed files with 100 additions and 0 deletions
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1
hw/vfio/pci-quirks.c
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@ -1259,6 +1259,7 @@ void vfio_bar_quirk_setup(VFIOPCIDevice *vdev, int nr)
vfio_probe_nvidia_bar0_quirk(vdev, nr);
vfio_probe_rtl8168_bar2_quirk(vdev, nr);
#ifdef CONFIG_VFIO_IGD
vfio_probe_igd_bar0_quirk(vdev, nr);
vfio_probe_igd_bar4_quirk(vdev, nr);
#endif
}