linux-kernel - Re: [PATCH v3 2/4] drivers/iommu: Add calls for IOMMU_DEBUG

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Message-ID: <07434771-3233-4c88-b505-ee02da72c905@linux.intel.com>
Date: Tue, 25 Nov 2025 15:35:08 +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 2/4] drivers/iommu: Add calls for IOMMU_DEBUG_PAGEALLOC

On 11/25/25 04:08, 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 | 26 +++++++++++++
>   drivers/iommu/iommu.c                 | 12 +++++-
>   include/linux/iommu-debug-pagealloc.h | 56 +++++++++++++++++++++++++++
>   3 files changed, 92 insertions(+), 2 deletions(-)
> 

Remove "drivers/" from the commit title.

$ git log --oneline drivers/iommu/iommu.c

[...]
> diff --git a/include/linux/iommu-debug-pagealloc.h b/include/linux/iommu-debug-pagealloc.h
> index 83e64d70bf6c..454303ec09c2 100644
> --- a/include/linux/iommu-debug-pagealloc.h
> +++ b/include/linux/iommu-debug-pagealloc.h
> @@ -8,10 +8,66 @@
>   #ifndef __LINUX_IOMMU_DEBUG_PAGEALLOC_H
>   #define __LINUX_IOMMU_DEBUG_PAGEALLOC_H
>   
> +struct iommu_domain;
> +
>   #ifdef CONFIG_IOMMU_DEBUG_PAGEALLOC
>   
> +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,
> +			       unsigned long iova, size_t size);
> +void __iommu_debug_unmap_end(struct iommu_domain *domain,
> +			     unsigned long iova, size_t size, size_t unmapped);
> +
> +static inline void iommu_debug_map(struct iommu_domain *domain,
> +				   phys_addr_t phys, size_t size)
> +{
> +	if (static_branch_unlikely(&iommu_debug_initialized))
> +		__iommu_debug_map(domain, phys, size);
> +}
> +
> +static inline void iommu_debug_unmap_begin(struct iommu_domain *domain,
> +					   unsigned long iova, size_t size)
> +{
> +	if (static_branch_unlikely(&iommu_debug_initialized))
> +		__iommu_debug_unmap_begin(domain, iova, size);
> +}
> +
> +static inline void iommu_debug_unmap_end(struct iommu_domain *domain,
> +					 unsigned long iova, size_t size,
> +					 size_t unmapped)
> +{
> +	if (static_branch_unlikely(&iommu_debug_initialized))
> +		__iommu_debug_unmap_end(domain, iova, size, unmapped);
> +}
> +
> +void iommu_debug_init(void);
> +
> +#else
> +static inline void iommu_debug_map(struct iommu_domain *domain,
> +				   phys_addr_t phys, size_t size)
> +{
> +}
> +
> +static inline void iommu_debug_unmap_begin(struct iommu_domain *domain,
> +					   unsigned long iova, size_t size)
> +{
> +}
> +
> +static inline void iommu_debug_unmap_end(struct iommu_domain *domain,
> +					 unsigned long iova, size_t size,
> +					 size_t unmapped)
> +{
> +}
> +
> +static inline void iommu_debug_init(void)
> +{
> +}

I suppose that all these should go to drivers/iommu/iommu-priv.h, as
they are for use in other files inside the IOMMU subsystem.

> +
>   #endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */
>   
>   #endif /* __LINUX_IOMMU_DEBUG_PAGEALLOC_H */

Thanks,
baolu