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

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Message-ID: <20251211125928.3258905-5-smostafa@google.com>
Date: Thu, 11 Dec 2025 12:59:28 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: linux-mm@...ck.org, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org
Cc: corbet@....net, joro@...tes.org, will@...nel.org, robin.murphy@....com, 
	akpm@...ux-foundation.org, vbabka@...e.cz, surenb@...gle.com, mhocko@...e.com, 
	jackmanb@...gle.com, hannes@...xchg.org, ziy@...dia.com, david@...hat.com, 
	lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, rppt@...nel.org, 
	xiaqinxin@...wei.com, baolu.lu@...ux.intel.com, rdunlap@...radead.org, 
	Mostafa Saleh <smostafa@...gle.com>
Subject: [PATCH v4 4/4] iommu: debug-pagealloc: Check mapped/unmapped kernel memory

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@...gle.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