linux-kernel - Re: [PATCH v5 2/4] iommu: Add calls for IOMMU_DEBUG

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Message-ID: <390a15a8-e530-46ee-a42c-cbb3170692df@linux.intel.com>
Date: Wed, 7 Jan 2026 13:48:36 +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, rdunlap@...radead.org
Subject: Re: [PATCH v5 2/4] iommu: Add calls for IOMMU_DEBUG_PAGEALLOC

On 1/7/26 00:21, Mostafa Saleh wrote:
> Add calls for the new iommu debug config IOMMU_DEBUG_PAGEALLOC:
> - iommu_debug_init: Enable the debug mode if configured by the user.
> - iommu_debug_map: Track iommu pages mapped, using physical address.
> - iommu_debug_unmap_begin: Track start of iommu unmap operation, with
>    IOVA and size.
> - iommu_debug_unmap_end: Track the end of unmap operation, passing the
>    actual unmapped size versus the tracked one at unmap_begin.
> 
> We have to do the unmap_begin/end as once pages are unmapped we lose
> the information of the physical address.
> This is racy, but the API is racy by construction as it uses refcounts
> and doesn't attempt to lock/synchronize with the IOMMU API as that will
> be costly, meaning that possibility of false negative exists.
> 
> Signed-off-by: Mostafa Saleh<smostafa@...gle.com>
> ---
>   drivers/iommu/iommu-debug-pagealloc.c | 28 +++++++++++++
>   drivers/iommu/iommu-priv.h            | 58 +++++++++++++++++++++++++++
>   drivers/iommu/iommu.c                 | 11 ++++-
>   include/linux/iommu-debug-pagealloc.h |  1 +
>   4 files changed, 96 insertions(+), 2 deletions(-)

Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>