Re: [PATCH v4 1/4] iommu: Add page_ext for IOMMU_DEBUG_PAGEALLOC

[Mostafa Saleh <smostafa@google.com>]

On Fri, Dec 12, 2025 at 10:17:11AM +0800, Baolu Lu wrote:
> On 12/11/25 20:59, Mostafa Saleh wrote:
> > Add a new config IOMMU_DEBUG_PAGEALLOC, which registers new data to
> > page_ext.
> > 
> > This config will be used by the IOMMU API to track pages mapped in
> > the IOMMU to catch drivers trying to free kernel memory that they
> > still map in their domains, causing all types of memory corruption.
> > 
> > This behaviour is disabled by default and can be enabled using
> > kernel cmdline iommu.debug_pagealloc.
> > 
> > Signed-off-by: Mostafa Saleh <smostafa@google.com>
> > ---
> >   .../admin-guide/kernel-parameters.txt         |  9 ++++++
> >   drivers/iommu/Kconfig                         | 19 +++++++++++
> >   drivers/iommu/Makefile                        |  1 +
> >   drivers/iommu/iommu-debug-pagealloc.c         | 32 +++++++++++++++++++
> >   include/linux/iommu-debug-pagealloc.h         | 17 ++++++++++
> >   mm/page_ext.c                                 |  4 +++
> >   6 files changed, 82 insertions(+)
> >   create mode 100644 drivers/iommu/iommu-debug-pagealloc.c
> >   create mode 100644 include/linux/iommu-debug-pagealloc.h
> 
> Do you need to update the MAINTAINERS file, since a new file (iommu-
> debug-pagealloc.h) is being added?
> 
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index a8d0afde7f85..d484d9d8d0a4 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2675,6 +2675,15 @@ Kernel parameters
> >   			1 - Bypass the IOMMU for DMA.
> >   			unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
> > +	iommu.debug_pagealloc=
> > +			[KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this
> > +			parameter enables the feature at boot time. By default, it
> > +			is disabled and the system behaves the same way as a kernel
> > +			built without CONFIG_IOMMU_DEBUG_PAGEALLOC.
> > +			Format: { "0" | "1" }
> > +			0 - Sanitizer disabled.
> > +			1 - Sanitizer enabled, expect runtime overhead.
> 
> "iommu.debug_pagealloc=0" has the same meaning as "unset". Would
> "iommu=debug_pagealloc" look more appropriate?

"iommu=" seems to be x86 specific. I was following the pattern for
"iommu.passthrough=", "iommu.strict=" and also as "debug_pagealloc="
has it's own command line, it made sense to design this way.

Thanks,
Mostafa

> 
> > +
> >   	io7=		[HW] IO7 for Marvel-based Alpha systems
> >   			See comment before marvel_specify_io7 in
> >   			arch/alpha/kernel/core_marvel.c.
> 
> [ ... ]
> 
> Other changes look good to me.
> 
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>