[PATCH 1/2] mm/page_ext: Add page_ext_get_phys()

Mostafa Saleh
2026-01-19T14:22:53Z

In the next patches, IOMMU code will add data to page_ext.
The IOMMU code would operate on physical addresses which
can be outside of system RAM.

Add a new function page_ext_get_phys() to abstract the logic of
checking the address and returning the page_ext.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
include/linux/page_ext.h | 6 ++++++
mm/page_ext.c | 23 +++++++++++++++++++++++
2 files changed, 29 insertions(+)

diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index 76c817162d2f..bd373496e166 100644
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -93,6 +93,7 @@ static inline bool page_ext_iter_next_fast_possible(unsigned long next_pfn)
#endif

extern struct page_ext *page_ext_get(const struct page *page);
+extern struct page_ext *page_ext_get_phys(phys_addr_t phys);
extern void page_ext_put(struct page_ext *page_ext);
extern struct page_ext *page_ext_lookup(unsigned long pfn);

@@ -215,6 +216,11 @@ static inline struct page_ext *page_ext_get(const struct page *page)
return NULL;
}

+static inline struct page_ext *page_ext_get_phys(phys_addr_t phys)
+{
+ return NULL;
+}
+
static inline void page_ext_put(struct page_ext *page_ext)
{
}
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 297e4cd8ce90..5fe65a0ac4f3 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -538,6 +538,29 @@ struct page_ext *page_ext_get(const struct page *page)
return page_ext;
}

+/**
+ * page_ext_get_phys() - Get the page_ext structure for a physical address.
+ * @phys: The physical address to query.
+ *
+ * This function safely gets the `struct page_ext` associated with a given
+ * physical address. It performs validation to ensure the address corresponds
+ * to a valid, online struct page before attempting to access it.
+ * It should return NULL for (MMIO, ZONE_DEVICE, holes, offline memory)
+ *
+ * Return: NULL if no page_ext exists for this physical address.
+ * Context: Any context. Caller may not sleep until they have called
+ * page_ext_put().
+ */
+struct page_ext *page_ext_get_phys(phys_addr_t phys)
+{
+ struct page *page = pfn_to_online_page(__phys_to_pfn(phys));
+
+ if (!page)
+ return NULL;
+
+ return page_ext_get(page);
+}
+
/**
* page_ext_put() - Working with page extended information is done.
* @page_ext: Page extended information received from page_ext_get().
--
2.52.0.457.g6b5491de43-goog