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

[Baolu Lu]

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?

> +#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>