Re: [PATCH v4 4/4] iommu: debug-pagealloc: Check mapped/unmapped kernel memory

[Mostafa Saleh]

On Fri, Dec 12, 2025 at 10:51:24AM +0800, Baolu Lu wrote:
> On 12/11/25 20:59, Mostafa Saleh wrote:
> > Now, as the page_ext holds count of IOMMU mappings, we can use it to
> > assert that any page allocated/freed is indeed not in the IOMMU.
> > 
> > The sanitizer doesn’t protect against mapping/unmapping during this
> > period. However, that’s less harmful as the page is not used by the
> > kernel.
> > 
> > Signed-off-by: Mostafa Saleh <smostafa@xxxxxxxxxx>
> > ---
> >   drivers/iommu/iommu-debug-pagealloc.c | 23 +++++++++++++++++++++++
> >   include/linux/iommu-debug-pagealloc.h | 14 ++++++++++++++
> >   include/linux/mm.h                    |  5 +++++
> >   3 files changed, 42 insertions(+)
> 
> [...]
> 
> > diff --git a/include/linux/iommu-debug-pagealloc.h b/include/linux/iommu-debug-pagealloc.h
> > index a439d6815ca1..46c3c1f70150 100644
> > --- a/include/linux/iommu-debug-pagealloc.h
> > +++ b/include/linux/iommu-debug-pagealloc.h
> > @@ -13,6 +13,20 @@ DECLARE_STATIC_KEY_FALSE(iommu_debug_initialized);
> >   extern struct page_ext_operations page_iommu_debug_ops;
> > +void __iommu_debug_check_unmapped(const struct page *page, int numpages);
> > +
> > +static inline void iommu_debug_check_unmapped(const struct page *page, int numpages)
> > +{
> > +	if (static_branch_unlikely(&iommu_debug_initialized))
> > +		__iommu_debug_check_unmapped(page, numpages);
> > +}
> 
> Same here, possible to make iommu_debug_initialized static?

This also is similar to the iommu ones to reduce overhead, the main
feature have the same pattern with "_debug_pagealloc_enabled" static
key.

Thanks,
Mostafa

> 
> > +#else
> > +static inline void iommu_debug_check_unmapped(const struct page *page,
> > +					      int numpages)
> > +{
> > +}
> > +
> >   #endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */
> >   #endif /* __LINUX_IOMMU_DEBUG_PAGEALLOC_H */
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 7a1819c20643..3763b71a7d3e 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -36,6 +36,7 @@
> >   #include <linux/rcuwait.h>
> >   #include <linux/bitmap.h>
> >   #include <linux/bitops.h>
> > +#include <linux/iommu-debug-pagealloc.h>
> >   struct mempolicy;
> >   struct anon_vma;
> > @@ -4133,12 +4134,16 @@ extern void __kernel_map_pages(struct page *page, int numpages, int enable);
> >   #ifdef CONFIG_DEBUG_PAGEALLOC
> >   static inline void debug_pagealloc_map_pages(struct page *page, int numpages)
> >   {
> > +	iommu_debug_check_unmapped(page, numpages);
> > +
> >   	if (debug_pagealloc_enabled_static())
> >   		__kernel_map_pages(page, numpages, 1);
> >   }
> >   static inline void debug_pagealloc_unmap_pages(struct page *page, int numpages)
> >   {
> > +	iommu_debug_check_unmapped(page, numpages);
> > +
> >   	if (debug_pagealloc_enabled_static())
> >   		__kernel_map_pages(page, numpages, 0);
> >   }
> 
> Other changes look good to me,
> 
> Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>