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a="62504927" X-IronPort-AV: E=Sophos;i="6.19,252,1754982000"; d="scan'208";a="62504927" X-CSE-ConnectionGUID: pN/Ux4sCQkOCn6iu8FWVmQ== X-CSE-MsgGUID: AanNRT4BQNSgSrO+k0UBsw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,252,1754982000"; d="scan'208";a="183986151" From: Zhenzhong Duan To: qemu-devel@nongnu.org Cc: alex.williamson@redhat.com, clg@redhat.com, eric.auger@redhat.com, mst@redhat.com, jasowang@redhat.com, peterx@redhat.com, ddutile@redhat.com, jgg@nvidia.com, nicolinc@nvidia.com, skolothumtho@nvidia.com, joao.m.martins@oracle.com, clement.mathieu--drif@eviden.com, kevin.tian@intel.com, yi.l.liu@intel.com, chao.p.peng@intel.com, Zhenzhong Duan Subject: [PATCH v7 23/23] docs/devel: Add IOMMUFD nesting documentation Date: Fri, 24 Oct 2025 04:43:47 -0400 Message-ID: <20251024084349.102322-24-zhenzhong.duan@intel.com> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20251024084349.102322-1-zhenzhong.duan@intel.com> References: <20251024084349.102322-1-zhenzhong.duan@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" Add documentation about using IOMMUFD backed VFIO device with intel_iommu w= ith x-flts=3Don. Suggested-by: Yi Liu Signed-off-by: Zhenzhong Duan --- docs/devel/vfio-iommufd.rst | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/docs/devel/vfio-iommufd.rst b/docs/devel/vfio-iommufd.rst index 3d1c11f175..f1e4d940e6 100644 --- a/docs/devel/vfio-iommufd.rst +++ b/docs/devel/vfio-iommufd.rst @@ -164,3 +164,28 @@ RAM discarding for mdev. =20 ``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 with x-flts=3Don +------------------------------------- + +Only IOMMUFD backed VFIO device is supported when intel_iommu is configured +with x-flts=3Don, for legacy container backed VFIO device, below error sho= ws: + +.. code-block:: none + + qemu-system-x86_64: -device vfio-pci,host=3D0000:02:00.0: vfio 0000:02= :00.0: Failed to set vIOMMU: Need IOMMUFD backend when x-flts=3Don + +VFIO device under PCI bridge is unsupported, use PCIE bridge if necessary, +or else below error shows: + +.. code-block:: none + + qemu-system-x86_64: -device vfio-pci,host=3D0000:02:00.0,bus=3Dbridge1= ,iommufd=3Diommufd0: vfio 0000:02:00.0: Failed to set vIOMMU: Host device u= nder PCI bridge is unsupported when x-flts=3Don + +If host IOMMU has ERRATA_772415_SPR17, kexec or reboot from "intel_iommu= =3Don,sm_on" +to "intel_iommu=3Don,sm_off" in guest is also unsupported. Configure scala= ble mode +off as below if it's not needed by guest. + +.. code-block:: bash + + -device intel-iommu,x-scalable-mode=3Doff --=20 2.47.1