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

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Message-ID: <5d7a305e-d6b6-49dc-ab1d-bddd1339d4a7@infradead.org>
Date: Mon, 24 Nov 2025 17:31:12 -0800
From: Randy Dunlap <rdunlap@...radead.org>
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

I missed one other thing:

On 11/24/25 3:13 PM, Randy Dunlap wrote:
> 
> 
> On 11/24/25 12:08 PM, 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/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 6c42061ca20e..dddf435a1c11 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -2557,6 +2557,12 @@
>>  			1 - Bypass the IOMMU for DMA.
>>  			unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
>>  
>> +	iommu.debug_pagealloc=

Please note what format the option parameter value takes and possible values,
like iommu.passthrough above here in the kernel-parameters.txt file.

>> +			[KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this
>> +			parameter enables the feature at boot time. By default, it
>> +			is disabled and the system behave the same way as a kernel
> 
> 			                           behaves
> 
>> +			built without CONFIG_IOMMU_DEBUG_PAGEALLOC.
>> +
>>  	io7=		[HW] IO7 for Marvel-based Alpha systems
>>  			See comment before marvel_specify_io7 in
>>  			arch/alpha/kernel/core_marvel.c.
> 
> 

-- 
~Randy