Re: [PATCH v2] docs: Add '-device intel-iommu' entry

[Maxim Levitsky <mlevitsk@redhat.com>]

On Wed, 2021-07-07 at 11:41 -0400, Peter Xu wrote:
> The parameters of intel-iommu device are non-trivial to understand.  Add an
> entry for it so that people can reference to it when using.
> 
> There're actually a few more options there, but I hide them explicitly because
> they shouldn't be used by normal QEMU users.
> 
> Cc: Chao Yang <chayang@redhat.com>
> Cc: Lei Yang <leiyang@redhat.com>
> Cc: Jing Zhao <jinzhao@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Reviewed-by: Jason Wang <jasowang@redhat.com>
> Reviewed-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> v2:
> - Drop "in the guest" in intremap entry [Jason]
> - Explain how the default value of intremap is chosen [Eric]
> - Add r-bs for Jason and Yi
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  qemu-options.hx | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 8965dabc83..0fcc8973dd 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -926,6 +926,39 @@ SRST
>  
>  ``-device pci-ipmi-bt,bmc=id``
>      Like the KCS interface, but defines a BT interface on the PCI bus.
> +
> +``-device intel-iommu[,option=...]``
> +    This is only supported by ``-machine q35``, which will enable Intel VT-d
> +    emulation within the guest.  It supports below options:
> +
> +    ``intremap=on|off`` (default: auto)
> +        This enables interrupt remapping feature.  It's required to enable
> +        complete x2apic.  Currently it only supports kvm kernel-irqchip modes
> +        ``off`` or ``split``, while full kernel-irqchip is not yet supported.
> +        The default value is "auto", which will be decided by the mode of
> +        kernel-irqchip.
> +
> +    ``caching-mode=on|off`` (default: off)
> +        This enables caching mode for the VT-d emulated device.  When
> +        caching-mode is enabled, each guest DMA buffer mapping will generate an
> +        IOTLB invalidation from the guest IOMMU driver to the vIOMMU device in
> +        a synchronous way.  It is required for ``-device vfio-pci`` to work
> +        with the VT-d device, because host assigned devices requires to setup
> +        the DMA mapping on the host before guest DMA starts.
> +
> +    ``device-iotlb=on|off`` (default: off)
> +        This enables device-iotlb capability for the emulated VT-d device.  So
> +        far virtio/vhost should be the only real user for this parameter,
> +        paired with ats=on configured for the device.
> +
> +    ``aw-bits=39|48`` (default: 39)
> +        This decides the address width of IOVA address space.  The address
> +        space has 39 bits width for 3-level IOMMU page tables, and 48 bits for
> +        4-level IOMMU page tables.
> +
> +    Please also refer to the wiki page for general scenarios of VT-d
> +    emulation in QEMU: https://wiki.qemu.org/Features/VT-d.
> +
>  ERST
>  
>  DEF("name", HAS_ARG, QEMU_OPTION_name,

As far as I know this looks very good.
Thanks for doing this!

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky