On Wed, Jul 07, 2021 at 11:29:47AM +0200, Eric Auger wrote: > Hi Peter, Hi, Eric,
> > 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?) Will do. > > + > > + ``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? I used "virtio/vhost" because vhost is only one type of virtio backend, so normally they should be used in pair. Also, the "ats=on" parameter should be an option to virtio frontend rather than vhost, hence I mentioned both. > > + 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? Caching mode check is done in vtd_machine_done_notify_one(). I think there's no such check for vhost, however iirc vhost should work with/without ats=on; I did't check deeper. > > + > > + ``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 for taking a look! -- Peter Xu