linux-kernel - Re: [PATCH] genpt: Make GENERIC

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Message-ID: <20251120193326.GB233636@ziepe.ca>
Date: Thu, 20 Nov 2025 15:33:26 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	KUnit Development <kunit-dev@...glegroups.com>,
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH] genpt: Make GENERIC_PT invisible

On Thu, Nov 20, 2025 at 07:31:10PM +0100, Geert Uytterhoeven wrote:
> Hi Jason,
> 
> CC kunit
> 
> On Thu, 20 Nov 2025 at 18:07, Jason Gunthorpe <jgg@...pe.ca> wrote:
> > On Thu, Nov 20, 2025 at 12:49:33PM -0400, Jason Gunthorpe wrote:
> > > On Wed, Nov 12, 2025 at 03:08:05PM +0100, Geert Uytterhoeven wrote:
> > > > There is no point in asking the user about the Generic Radix Page
> > > > Table API:
> > > >   - All IOMMU drivers that use this API already select GENERIC_PT when
> > > >     needed,
> > > >   - Most users probably do not know what to answer anyway.
> > > >
> > > > Fixes: 7c5b184db7145fd4 ("genpt: Generic Page Table base API")
> > > > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > > > ---
> > > >  drivers/iommu/generic_pt/Kconfig | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> >
> > Actually, it doesn't work :\
> >
> > $ tools/testing/kunit/kunit.py run --build_dir build_kunit_x86_64 --arch x86_64 --kunitconfig ./drivers/iommu/generic_pt/.kunitconfig
> > [13:01:26] Configuring KUnit Kernel ...
> > [13:01:26] Building KUnit Kernel ...
> > Populating config with:
> > $ make ARCH=x86_64 O=build_kunit_x86_64 olddefconfig
> > Building with:
> > $ make all compile_commands.json scripts_gdb ARCH=x86_64 O=build_kunit_x86_64 --jobs=20
> > ERROR:root:Not all Kconfig options selected in kunitconfig were in the generated .config.
> > This is probably due to unsatisfied dependencies.
> > Missing: CONFIG_IOMMUFD_TEST=y, CONFIG_DEBUG_GENERIC_PT=y, CONFIG_IOMMU_PT_VTDSS=y, CONFIG_IOMMU_PT=y, CONFIG_IOMMU_PT_AMDV1=y, CONFIG_IOMMU_PT_X86_64=y, CONFIG_GENERIC_PT=y, CONFIG_IOMMU_PT_KUNIT_TEST=y
> >
> > Can you add this hunk and send a v2?
> >
> > --- a/drivers/iommu/generic_pt/.kunitconfig
> > +++ b/drivers/iommu/generic_pt/.kunitconfig
> > @@ -1,4 +1,5 @@
> >  CONFIG_KUNIT=y
> > +CONFIG_COMPILE_TEST=y
> >  CONFIG_GENERIC_PT=y
> >  CONFIG_DEBUG_GENERIC_PT=y
> >  CONFIG_IOMMU_PT=y
> 
> Do you really want to enable CONFIG_COMPILE_TEST in a .kunitconfig?

IDK, why not?

> Hm, that .kunitconfig already enables IOMMUFD_TEST, which is
> documented to be dangerous (why?)

It builds in a kernel module with a uapi that is kind of unsafe.

Though, hmm, maybe that is some weird a leftover I don't recall that
this kunit needed IOMMUFD_TEST stanza at all..

>  and already enabled by allyesconfig (except on GENERIC_ATOMIC64
> architectures).  

I guess allyesconfig would do that.

> IOMMUFD_TEST cannot select GENERIC_PT, as that would lead to a
> recursive dependency (and I am not a huge fan of test code
> auto-enabling extra attack surfaces^W^W functionality).

Yes

> Or perhaps:
> 
> -       bool "Generic Radix Page Table"
> +       bool "Generic Radix Page Table" if COMPILE_TEST || KUNIT
> 
> ?

It would work, that does seem like a better choice if someone wants to
make the kunit run in a normal disto kernel.

Thanks,
Jason