Hi Peter, On 6/11/21 8:55 PM, 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 <chay...@redhat.com> > Cc: Lei Yang <leiy...@redhat.com> > Cc: Jing Zhao <jinz...@redhat.com> > Cc: Jason Wang <jasow...@redhat.com> > Cc: Michael S. Tsirkin <m...@redhat.com> > Cc: Alex Williamson <alex.william...@redhat.com> > Signed-off-by: Peter Xu <pet...@redhat.com> > --- > qemu-options.hx | 32 ++++++++++++++++++++++++++++++++ > 1 file changed, 32 insertions(+) > > diff --git a/qemu-options.hx b/qemu-options.hx > index 14258784b3a..4bb04243907 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -926,6 +926,38 @@ 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 in the guest. It's required > + to enable complete x2apic. Currently it only supports kvm > + kernel-irqchip modes ``off`` or ``split``. Full kernel-irqchip is > not > + yet supported. maybe explain how the default is chosen (based on kernel-irqhcip mode?) > + > + ``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, I thought if was needed for vhost. What is the usage for virtio? > + paired with ats=on configured for the device. What is not obvious to me is whether there is a kind of diagnosis whether device-iotlb and caching mode settings are consistent with vfio/vhost usage. Does qemu exit if there is inconsistency? > + > + ``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, > Besides, it is quite useful.
Thanks Eric