From: Zhenzhong Duan Date: Tue, 6 Jan 2026 06:13:01 +0000 (-0500) Subject: docs/devel: Add IOMMUFD nesting documentation X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ce1e8716801f4f1b5f31fb59e0b221bf0851121b;p=thirdparty%2Fqemu.git docs/devel: Add IOMMUFD nesting documentation Add documentation about using IOMMUFD backed VFIO device with intel_iommu with x-flts=on. Suggested-by: Yi Liu Signed-off-by: Zhenzhong Duan Reviewed-by: Eric Auger Reviewed-by: Yi Liu Reviewed-by: Michael S. Tsirkin Link: https://lore.kernel.org/qemu-devel/20260106061304.314546-20-zhenzhong.duan@intel.com Signed-off-by: Cédric Le Goater --- diff --git a/docs/devel/vfio-iommufd.rst b/docs/devel/vfio-iommufd.rst index b37098e1b6..2d6e60dce1 100644 --- a/docs/devel/vfio-iommufd.rst +++ b/docs/devel/vfio-iommufd.rst @@ -152,3 +152,20 @@ RAM discarding for mdev. ``vfio-ap`` and ``vfio-ccw`` devices don't have same issue as their backend devices are always mdev and RAM discarding is force enabled. + +Usage with intel_iommu featuring x-flts=on +------------------------------------------ + +Only IOMMUFD backed VFIO device is supported when intel_iommu is configured +with x-flts=on, for legacy container backed VFIO device, below error shows: + +.. code-block:: none + + qemu-system-x86_64: -device vfio-pci,host=0000:02:00.0: vfio 0000:02:00.0: Failed to set vIOMMU: Need IOMMUFD backend when x-flts=on + +VFIO device under PCI bridge is unsupported, use PCIE bridge if necessary, +otherwise below error shows: + +.. code-block:: none + + qemu-system-x86_64: -device vfio-pci,host=0000:02:00.0,bus=bridge1,iommufd=iommufd0: vfio 0000:02:00.0: Failed to set vIOMMU: Host device downstream to a PCI bridge is unsupported when x-flts=on