amd_iommu: Document '-device amd-iommu' common options

Document the common parameters used when emulating AMD vIOMMU.
Besides the two amd-iommu specific options: 'xtsup' and 'dma-remap', the
the generic x86 IOMMU option 'intremap' is also included, since it is
typically specified in QEMU command line examples and mailing list threads.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20250919213515.917111-3-alejandro.j.jimenez@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/qemu-options.hx b/qemu-options.hx
index 3ff10ec09d9c6a78cb189d757235f5bd81c0f931..9b4e870350aadd5bd9120ae3c44081c8e3e67ba8 100644 (file)
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1238,6 +1238,29 @@ SRST
         Accepts either the default root complex (pcie.0) or a
         pxb-pcie based root complex.
 
+``-device amd-iommu[,option=...]``
+    Enables emulation of an AMD-Vi I/O Memory Management Unit (IOMMU).
+    Only available with ``-machine q35``, it supports the following options:
+
+    ``dma-remap=on|off`` (default: off)
+        Support for DMA address translation and access permission checking for
+        guests attaching passthrough devices to paging domains, using the AMD v1
+        I/O Page Table format. This enables ``-device vfio-pci,...`` to work
+        correctly with a guest using the DMA remapping feature of the vIOMMU.
+
+    ``intremap=on|off`` (default: auto)
+        Generic x86 IOMMU functionality implemented by ``amd-iommu`` device.
+        Enables interrupt remapping feature in guests, which is also required to
+        enable x2apic support.
+        Currently only available with ``kernel-irqchip=off|split``, it is
+        automatically enabled when either of those modes is in use, and disabled
+        with ``kernel-irqchip=on``.
+
+    ``xtsup=on|off`` (default: off)
+        Interrupt remapping table supports x2apic mode, enabling the use of
+        128-bit IRTE format with 32-bit destination field by the guest. Required
+        to support routing interrupts to vCPUs with APIC IDs larger than 0xff.
+
 ERST
 
 DEF("name", HAS_ARG, QEMU_OPTION_name,