[PATCH v2 0/2] iommu: debug-pagealloc: Remove pfn_valid() usage

[PATCH v2 0/2] iommu: debug-pagealloc: Remove pfn_valid() usage

[Mostafa Saleh]

This is a small fix for the new config IOMMU_DEBUG_PAGEALLOC based
on the discussion:
https://lore.kernel.org/linux-iommu/CAFgf54pBAUm3ao-UJksiuGKtvv4wzRyFq_uKwLe0H1ettO4DLQ@mail.gmail.com/

Where it was concluded that pfn_valid() is not enough to validate
physical addresses before access to page_ext.

The first patch introduces a new function in page_ext that takes a
physical address as an argument, and the second patch uses it instead
of calling pfn_valid() and phys_to_page()

Benchmarks with the new implementation can be found in:
https://lore.kernel.org/linux-iommu/20260114164322.787125-1-smostafa@google.com/

This series applies to iommu/core tree.

Changes on v2:
v1: https://lore.kernel.org/linux-iommu/20260119142246.3821052-1-smostafa@google.com/
- Rename page_ext_phys() to page_ext_from_phys()
- Reword comment and commit messages.

Mostafa Saleh (2):
  mm/page_ext: Add page_ext_get_from_phys()
  iommu: debug-pagealloc: Use page_ext_get_from_phys()

 drivers/iommu/iommu-debug-pagealloc.c | 31 ++++++++++++---------------
 include/linux/page_ext.h              |  6 ++++++
 mm/page_ext.c                         | 23 ++++++++++++++++++++
 3 files changed, 43 insertions(+), 17 deletions(-)

-- 
2.52.0.457.g6b5491de43-goog

[PATCH v2 1/2] mm/page_ext: Add page_ext_get_from_phys()

[Mostafa Saleh]

The IOMMU code operates on physical addresses which can be outside
of system RAM.

Add a new function page_ext_get_from_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..61e876e255e8 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_from_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_from_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..e2e92bd27ebd 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_from_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 returns NULL for MMIO, ZONE_DEVICE, holes and 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_from_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

Re: [PATCH v2 1/2] mm/page_ext: Add page_ext_get_from_phys()

[Vlastimil Babka]

On 1/20/26 10:19, Mostafa Saleh wrote:
> The IOMMU code operates on physical addresses which can be outside
> of system RAM.
> 
> Add a new function page_ext_get_from_phys() to abstract the logic of
> checking the address and returning the page_ext.
> 
> Signed-off-by: Mostafa Saleh <smostafa@google.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  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..61e876e255e8 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_from_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_from_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..e2e92bd27ebd 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_from_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 returns NULL for MMIO, ZONE_DEVICE, holes and 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_from_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().

[PATCH v2 2/2] iommu: debug-pagealloc: Use page_ext_get_from_phys()

[Mostafa Saleh]

Instead of calling pfn_valid() and then getting the page, call
the newly added function page_ext_get_from_phys(), which would
also check for MMIO and offline memory and return NULL in that
case.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
 drivers/iommu/iommu-debug-pagealloc.c | 31 ++++++++++++---------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c
index c080a38f45a4..80164df5bab1 100644
--- a/drivers/iommu/iommu-debug-pagealloc.c
+++ b/drivers/iommu/iommu-debug-pagealloc.c
@@ -30,14 +30,6 @@ struct page_ext_operations page_iommu_debug_ops = {
 	.need = need_iommu_debug,
 };
 
-static struct page_ext *get_iommu_page_ext(phys_addr_t phys)
-{
-	struct page *page = phys_to_page(phys);
-	struct page_ext *page_ext = page_ext_get(page);
-
-	return page_ext;
-}
-
 static struct iommu_debug_metadata *get_iommu_data(struct page_ext *page_ext)
 {
 	return page_ext_data(page_ext, &page_iommu_debug_ops);
@@ -45,18 +37,26 @@ static struct iommu_debug_metadata *get_iommu_data(struct page_ext *page_ext)
 
 static void iommu_debug_inc_page(phys_addr_t phys)
 {
-	struct page_ext *page_ext = get_iommu_page_ext(phys);
-	struct iommu_debug_metadata *d = get_iommu_data(page_ext);
+	struct page_ext *page_ext = page_ext_from_phys(phys);
+	struct iommu_debug_metadata *d;
+
+	if (!page_ext)
+		return;
 
+	d = get_iommu_data(page_ext);
 	WARN_ON(atomic_inc_return_relaxed(&d->ref) <= 0);
 	page_ext_put(page_ext);
 }
 
 static void iommu_debug_dec_page(phys_addr_t phys)
 {
-	struct page_ext *page_ext = get_iommu_page_ext(phys);
-	struct iommu_debug_metadata *d = get_iommu_data(page_ext);
+	struct page_ext *page_ext = page_ext_from_phys(phys);
+	struct iommu_debug_metadata *d;
+
+	if (!page_ext)
+		return;
 
+	d = get_iommu_data(page_ext);
 	WARN_ON(atomic_dec_return_relaxed(&d->ref) < 0);
 	page_ext_put(page_ext);
 }
@@ -104,11 +104,8 @@ void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t siz
 	if (WARN_ON(!phys || check_add_overflow(phys, size, &end)))
 		return;
 
-	for (off = 0 ; off < size ; off += page_size) {
-		if (!pfn_valid(__phys_to_pfn(phys + off)))
-			continue;
+	for (off = 0 ; off < size ; off += page_size)
 		iommu_debug_inc_page(phys + off);
-	}
 }
 
 static void __iommu_debug_update_iova(struct iommu_domain *domain,
@@ -123,7 +120,7 @@ static void __iommu_debug_update_iova(struct iommu_domain *domain,
 	for (off = 0 ; off < size ; off += page_size) {
 		phys_addr_t phys = iommu_iova_to_phys(domain, iova + off);
 
-		if (!phys || !pfn_valid(__phys_to_pfn(phys)))
+		if (!phys)
 			continue;
 
 		if (inc)
-- 
2.52.0.457.g6b5491de43-goog

Re: [PATCH v2 0/2] iommu: debug-pagealloc: Remove pfn_valid() usage

[Jörg Rödel]

On Tue, Jan 20, 2026 at 09:19:24AM +0000, Mostafa Saleh wrote:
> Mostafa Saleh (2):
>   mm/page_ext: Add page_ext_get_from_phys()
>   iommu: debug-pagealloc: Use page_ext_get_from_phys()
> 
>  drivers/iommu/iommu-debug-pagealloc.c | 31 ++++++++++++---------------
>  include/linux/page_ext.h              |  6 ++++++
>  mm/page_ext.c                         | 23 ++++++++++++++++++++
>  3 files changed, 43 insertions(+), 17 deletions(-)

Applied, thanks.