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

Mostafa Saleh posted 4 patches 4 days, 16 hours ago
[PATCH v4 4/4] iommu: debug-pagealloc: Check mapped/unmapped kernel memory
Posted by Mostafa Saleh 4 days, 16 hours ago 
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@google.com>
---
 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/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c
index 4639cf9518e6..424e00cd103b 100644
--- a/drivers/iommu/iommu-debug-pagealloc.c
+++ b/drivers/iommu/iommu-debug-pagealloc.c
@@ -9,6 +9,7 @@
 #include <linux/iommu-debug-pagealloc.h>
 #include <linux/kernel.h>
 #include <linux/page_ext.h>
+#include <linux/page_owner.h>
 
 #include "iommu-priv.h"
 
@@ -73,6 +74,28 @@ static size_t iommu_debug_page_size(struct iommu_domain *domain)
 	return 1UL << __ffs(domain->pgsize_bitmap);
 }
 
+static bool iommu_debug_page_count(const struct page *page)
+{
+	unsigned int ref;
+	struct page_ext *page_ext = page_ext_get(page);
+	struct iommu_debug_metadata *d = get_iommu_data(page_ext);
+
+	ref = atomic_read(&d->ref);
+	page_ext_put(page_ext);
+	return ref != 0;
+}
+
+void __iommu_debug_check_unmapped(const struct page *page, int numpages)
+{
+	while (numpages--) {
+		if (WARN_ON(iommu_debug_page_count(page))) {
+			pr_warn("iommu: Detected page leak!\n");
+			dump_page_owner(page);
+		}
+		page++;
+	}
+}
+
 void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t size)
 {
 	size_t off, end;
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);
+}
+
+#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);
 }
-- 
2.52.0.223.gf5cc29aaa4-goog
Re: [PATCH v4 4/4] iommu: debug-pagealloc: Check mapped/unmapped kernel memory
Posted by Baolu Lu 4 days, 2 hours ago 
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@google.com>
> ---
>   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@linux.intel.com>
Re: [PATCH v4 4/4] iommu: debug-pagealloc: Check mapped/unmapped kernel memory
Posted by Mostafa Saleh 3 days, 10 hours ago 
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@google.com>
> > ---
> >   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@linux.intel.com>

Patchew 2.1-devel-b67e4c2

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