linux-kernel - Re: [PATCH v3 1/4] drivers/iommu: Add page_ext for IOMMU_DEBUG

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Message-ID: <5f85e519-5a05-4359-9904-06f16737e28b@linux.intel.com>
Date: Tue, 25 Nov 2025 15:17:47 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Mostafa Saleh <smostafa@...gle.com>, 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
Subject: Re: [PATCH v3 1/4] drivers/iommu: Add page_ext for
 IOMMU_DEBUG_PAGEALLOC

On 11/25/25 04:08, Mostafa Saleh wrote:
> Add a new config IOMMU_DEBUG_PAGEALLOC, which registers new data to
> page_ext.
> 
> This config will be used by the IOMMU API to track pages mapped in
> the IOMMU to catch drivers trying to free kernel memory that they
> still map in their domains, causing all types of memory corruption.
> 
> This behaviour is disabled by default and can be enabled using
> kernel cmdline iommu.debug_pagealloc.
> 
> Signed-off-by: Mostafa Saleh <smostafa@...gle.com>
> ---
>   .../admin-guide/kernel-parameters.txt         |  6 ++++
>   drivers/iommu/Kconfig                         | 19 +++++++++++
>   drivers/iommu/Makefile                        |  1 +
>   drivers/iommu/iommu-debug-pagealloc.c         | 32 +++++++++++++++++++
>   include/linux/iommu-debug-pagealloc.h         | 17 ++++++++++
>   mm/page_ext.c                                 |  4 +++
>   6 files changed, 79 insertions(+)
>   create mode 100644 drivers/iommu/iommu-debug-pagealloc.c
>   create mode 100644 include/linux/iommu-debug-pagealloc.h
> 

[..]

> diff --git a/include/linux/iommu-debug-pagealloc.h b/include/linux/iommu-debug-pagealloc.h
> new file mode 100644
> index 000000000000..83e64d70bf6c
> --- /dev/null
> +++ b/include/linux/iommu-debug-pagealloc.h
> @@ -0,0 +1,17 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2025 - Google Inc
> + * Author: Mostafa Saleh <smostafa@...gle.com>
> + * IOMMU API debug page alloc sanitizer
> + */
> +
> +#ifndef __LINUX_IOMMU_DEBUG_PAGEALLOC_H
> +#define __LINUX_IOMMU_DEBUG_PAGEALLOC_H
> +
> +#ifdef CONFIG_IOMMU_DEBUG_PAGEALLOC
> +
> +extern struct page_ext_operations page_iommu_debug_ops;

How about moving above to below mm/page_ext.c and remove iommu-debug-
pagealloc.h header file? ...

> +
> +#endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */
> +
> +#endif /* __LINUX_IOMMU_DEBUG_PAGEALLOC_H */
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index d7396a8970e5..297e4cd8ce90 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -11,6 +11,7 @@
>   #include <linux/page_table_check.h>
>   #include <linux/rcupdate.h>
>   #include <linux/pgalloc_tag.h>
> +#include <linux/iommu-debug-pagealloc.h>

... remove this include line and put the "extern" line here,

extern struct page_ext_operations page_iommu_debug_ops;

>   
>   /*
>    * struct page extension
> @@ -89,6 +90,9 @@ static struct page_ext_operations *page_ext_ops[] __initdata = {
>   #ifdef CONFIG_PAGE_TABLE_CHECK
>   	&page_table_check_ops,
>   #endif
> +#ifdef CONFIG_IOMMU_DEBUG_PAGEALLOC
> +	&page_iommu_debug_ops,
> +#endif
>   };
>   
>   unsigned long page_ext_size;

Or, put it directly in linux/iommu.h?

diff --git a/include/linux/iommu-debug-pagealloc.h 
b/include/linux/iommu-debug-pagealloc.h
index 87f593305465..b2b82cf032e6 100644
--- a/include/linux/iommu-debug-pagealloc.h
+++ b/include/linux/iommu-debug-pagealloc.h
@@ -14,8 +14,6 @@ struct iommu_domain;

  DECLARE_STATIC_KEY_FALSE(iommu_debug_initialized);

-extern struct page_ext_operations page_iommu_debug_ops;
-
  void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys,
                        size_t size);
  void __iommu_debug_unmap_begin(struct iommu_domain *domain,
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 801b2bd9e8d4..40133031985a 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -1185,6 +1185,10 @@ void iommu_detach_device_pasid(struct 
iommu_domain *domain,
                                struct device *dev, ioasid_t pasid);
  ioasid_t iommu_alloc_global_pasid(struct device *dev);
  void iommu_free_global_pasid(ioasid_t pasid);
+
+#ifdef CONFIG_IOMMU_DEBUG_PAGEALLOC
+extern struct page_ext_operations page_iommu_debug_ops;
+#endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */
  #else /* CONFIG_IOMMU_API */

  struct iommu_ops {};
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 297e4cd8ce90..345af8c9fcce 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -11,7 +11,7 @@
  #include <linux/page_table_check.h>
  #include <linux/rcupdate.h>
  #include <linux/pgalloc_tag.h>
-#include <linux/iommu-debug-pagealloc.h>
+#include <linux/iommu.h>

  /*
   * struct page extension

Thanks,
baolu