Re: [RFC 1/7] x86/iommu: make AMD-Vi and Intel VT-d support configurable

[Xenia Ragiadakou <burzalodowa@xxxxxxxxx>]

On 12/20/22 23:00, Andrew Cooper wrote:
> On 20/12/2022 8:57 pm, Xenia Ragiadakou wrote:
> > On 12/20/22 19:01, Jan Beulich wrote:
> > > On 19.12.2022 07:34, Xenia Ragiadakou wrote:
> > > > Currently, for x86 platforms, Xen does not provide to the users any
> > > > configuration control over the IOMMU support and can only be built with
> > > > both AMD and Intel IOMMU drivers enabled.
> > > > However, there are use cases, e.g in safety-critical systems, that
> > > > require
> > > > Xen to be able to be configured to exclude unused code. A smaller
> > > > tailored
> > > > configuration would help Xen to meet faster certification
> > > > requirements for
> > > > individual platforms.
> > > >
> > > > Introduce two new Kconfig options, AMD_IOMMU and INTEL_VTD, to allow
> > > > code
> > > > specific to each IOMMU technology to be separated and, when not
> > > > required,
> > > > stripped. AMD_IOMMU enables IOMMU support for platforms that
> > > > implement the
> > > > AMD I/O Virtualization Technology. INTEL_VTD enables IOMMU support for
> > > > platforms that implement the Intel Virtualization Technology for
> > > > Directed I/O.
> > > >
> > > > Since no functional change is intended regarding the default
> > > > configuration
> > > > of an x86 system, both options depend on x86 and default to 'y'.
> > > But do things also build successfully when one or both options are
> > > disabled?
> > > I have to say that I would be quite surprised if that worked without
> > > further
> > > adjustments. In which case initially these options want to be
> > > prompt-less,
> > > with the prompts only added once 'n' also works.
> > Without applying the whole series, disabling any of them or both won't
> > work. Ok.
> To do a multi-step implementation, you start with
>
> config FOO
>      bool y
Here, I think you mean def_bool y

> then rearrange them main code to use CONFIG_FOO as appropriate, then
> have a final patch that adds a Kconfig name, help text, etc which is
> what makes the config option user selectable and able to be turned off.
Thank you both, for pointing that out. I will fix it.

> ~Andrew
--
Xenia