Re: [PATCH] intel_iommu: Remove 'x-' prefix from 'x-scalable-mode' and 'x-flts' properties

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Mar 09, 2026 at 01:44:15PM +0100, Philippe Mathieu-Daudé wrote:
> Hi,
> 
> On 9/3/26 10:20, Zhenzhong Duan wrote:
> > We had 'x-scalable-mode' for more than 5 years and 'x-flts' for more than 1
> > year, it's fine to remove 'x-' now.
> > 
> > This is a prerequisite to enable intel_iommu's scalable mode and first stage
> > translation support in libvirt.
> > 
> > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> > ---
> >   docs/devel/vfio-iommufd.rst    | 10 +++++-----
> >   hw/i386/intel_iommu.c          |  8 ++++----
> >   hw/i386/intel_iommu_accel.c    |  4 ++--
> >   tests/qtest/intel-iommu-test.c |  2 +-
> >   4 files changed, 12 insertions(+), 12 deletions(-)
> > 
> > diff --git a/docs/devel/vfio-iommufd.rst b/docs/devel/vfio-iommufd.rst
> > index 78bcdffac7..5755532443 100644
> > --- a/docs/devel/vfio-iommufd.rst
> > +++ b/docs/devel/vfio-iommufd.rst
> > @@ -153,22 +153,22 @@ RAM discarding for mdev.
> >   ``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 featuring x-flts=on
> > +Usage with intel_iommu featuring flts=on
> >   ------------------------------------------
> >   Only IOMMUFD backed VFIO device is supported when intel_iommu is configured
> > -with x-flts=on, for legacy container backed VFIO device, below error shows:
> > +with flts=on, for legacy container backed VFIO device, below error shows:
> >   .. code-block:: none
> > -    qemu-system-x86_64: -device vfio-pci,host=0000:02:00.0: vfio 0000:02:00.0: Failed to set vIOMMU: Need IOMMUFD backend when x-flts=on
> > +    qemu-system-x86_64: -device vfio-pci,host=0000:02:00.0: vfio 0000:02:00.0: Failed to set vIOMMU: Need IOMMUFD backend when flts=on
> >   VFIO device under PCI bridge is unsupported, use PCIE bridge if necessary,
> >   otherwise below error shows:
> >   .. code-block:: none
> > -    qemu-system-x86_64: -device vfio-pci,host=0000:02:00.0,bus=bridge1,iommufd=iommufd0: vfio 0000:02:00.0: Failed to set vIOMMU: Host device downstream to a PCI bridge is unsupported when x-flts=on
> > +    qemu-system-x86_64: -device vfio-pci,host=0000:02:00.0,bus=bridge1,iommufd=iommufd0: vfio 0000:02:00.0: Failed to set vIOMMU: Host device downstream to a PCI bridge is unsupported when flts=on
> >   If host IOMMU has ERRATA_772415_SPR17, running guest with "intel_iommu=on,sm_off"
> >   is unsupported, kexec or reboot guest from "intel_iommu=on,sm_on" to
> > @@ -177,4 +177,4 @@ below if it's not needed by guest:
> >   .. code-block:: bash
> > -    -device intel-iommu,x-scalable-mode=off
> > +    -device intel-iommu,scalable-mode=off
> > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> > index d24ba989bf..001847ad37 100644
> > --- a/hw/i386/intel_iommu.c
> > +++ b/hw/i386/intel_iommu.c
> > @@ -4200,8 +4200,8 @@ static const Property vtd_properties[] = {
> >       DEFINE_PROP_UINT8("aw-bits", IntelIOMMUState, aw_bits,
> >                         VTD_HOST_ADDRESS_WIDTH),
> >       DEFINE_PROP_BOOL("caching-mode", IntelIOMMUState, caching_mode, FALSE),
> > -    DEFINE_PROP_BOOL("x-scalable-mode", IntelIOMMUState, scalable_mode, FALSE),
> > -    DEFINE_PROP_BOOL("x-flts", IntelIOMMUState, fsts, FALSE),
> 
> IMHO safer would be to officially deprecate these in
> docs/about/deprecated.rst and keeping them aliased until deprecation
> period expires. Other changes LGTM.

The purpose of using an 'x-' prefix for properties in QEMU is to declare
that they are subject to change with no warning, so we are free to change
them without any deprecation IMHO.

> > +    DEFINE_PROP_BOOL("scalable-mode", IntelIOMMUState, scalable_mode, FALSE),
> > +    DEFINE_PROP_BOOL("flts", IntelIOMMUState, fsts, FALSE),
> >       DEFINE_PROP_BOOL("snoop-control", IntelIOMMUState, snoop_control, false),
> >       DEFINE_PROP_BOOL("x-pasid-mode", IntelIOMMUState, pasid, false),
> >       DEFINE_PROP_BOOL("svm", IntelIOMMUState, svm, false),
> 

With regards,
Daniel
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