Re: [PATCH 1/2] iommu: Add __iommu_debug_unmap_phys() to drop refs by physical address

[Mostafa Saleh <smostafa@google.com>]

On Thu, Aug 27, 2026 at 10:58:54PM +0800, Yuanhe Shu wrote:
> The IOMMU_DEBUG_PAGEALLOC sanitizer takes a reference on each page at
> iommu_map() time, keyed by physical address, and the only way to drop
> them is the IOVA based iommu_debug_unmap_begin()/end().  A path that
> tears down a page table with mappings still installed has no IOVA to
> unmap with, so add a physical address based counterpart of
> __iommu_debug_map() for those paths, sharing the counting loop through
> __iommu_debug_update_phys().

But the IOVA can be calculated when walking the table from freeing
context or am I missing something?

Thanks,
Mostafa

> 
> Export the iommu_debug_initialized static key, as the generic_pt format
> code using these helpers can be built as a module.
> 
> Signed-off-by: Yuanhe Shu <xiangzao@linux.alibaba.com>
> ---
> Build tested as built-in and as a module (AMD_IOMMU=n,
> CONFIG_IOMMU_PT_AMDV1=m).
> 
>  drivers/iommu/iommu-debug-pagealloc.c | 30 ++++++++++++++++++++++++---
>  drivers/iommu/iommu-priv.h            | 24 +++++++++++++++++++++
>  2 files changed, 51 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c
> index 80164df5bab1..a2e55164e6a4 100644
> --- a/drivers/iommu/iommu-debug-pagealloc.c
> +++ b/drivers/iommu/iommu-debug-pagealloc.c
> @@ -15,6 +15,8 @@
>  
>  static bool needed;
>  DEFINE_STATIC_KEY_FALSE(iommu_debug_initialized);
> +/* The generic_pt format code using the key can be built as a module */
> +EXPORT_SYMBOL_GPL(iommu_debug_initialized);
>  
>  struct iommu_debug_metadata {
>  	atomic_t ref;
> @@ -96,7 +98,8 @@ void __iommu_debug_check_unmapped(const struct page *page, int numpages)
>  	}
>  }
>  
> -void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t size)
> +static void __iommu_debug_update_phys(struct iommu_domain *domain,
> +				      phys_addr_t phys, size_t size, bool inc)
>  {
>  	size_t off, end;
>  	size_t page_size = iommu_debug_page_size(domain);
> @@ -104,9 +107,30 @@ 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)
> -		iommu_debug_inc_page(phys + off);
> +	for (off = 0 ; off < size ; off += page_size) {
> +		if (inc)
> +			iommu_debug_inc_page(phys + off);
> +		else
> +			iommu_debug_dec_page(phys + off);
> +	}
> +}
> +
> +void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t size)
> +{
> +	__iommu_debug_update_phys(domain, phys, size, true);
> +}
> +
> +/*
> + * Physical address counterpart of __iommu_debug_map(), for teardown paths
> + * that destroy mapped entries without an IOVA.  The OAs must have been
> + * accounted by a prior iommu_map().
> + */
> +void __iommu_debug_unmap_phys(struct iommu_domain *domain, phys_addr_t phys,
> +			      size_t size)
> +{
> +	__iommu_debug_update_phys(domain, phys, size, false);
>  }
> +EXPORT_SYMBOL_GPL(__iommu_debug_unmap_phys);
>  
>  static void __iommu_debug_update_iova(struct iommu_domain *domain,
>  				      unsigned long iova, size_t size, bool inc)
> diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
> index aaffad5854fc..12528a40bcd8 100644
> --- a/drivers/iommu/iommu-priv.h
> +++ b/drivers/iommu/iommu-priv.h
> @@ -71,11 +71,18 @@ int iommu_replace_device_pasid(struct iommu_domain *domain,
>  
>  void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys,
>  		       size_t size);
> +void __iommu_debug_unmap_phys(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 bool iommu_debug_pagealloc_enabled(void)
> +{
> +	return static_branch_unlikely(&iommu_debug_initialized);
> +}
> +
>  static inline void iommu_debug_map(struct iommu_domain *domain,
>  				   phys_addr_t phys, size_t size)
>  {
> @@ -83,6 +90,13 @@ static inline void iommu_debug_map(struct iommu_domain *domain,
>  		__iommu_debug_map(domain, phys, size);
>  }
>  
> +static inline void iommu_debug_unmap_phys(struct iommu_domain *domain,
> +					  phys_addr_t phys, size_t size)
> +{
> +	if (static_branch_unlikely(&iommu_debug_initialized))
> +		__iommu_debug_unmap_phys(domain, phys, size);
> +}
> +
>  static inline void iommu_debug_unmap_begin(struct iommu_domain *domain,
>  					   unsigned long iova, size_t size)
>  {
> @@ -101,11 +115,21 @@ static inline void iommu_debug_unmap_end(struct iommu_domain *domain,
>  void iommu_debug_init(void);
>  
>  #else
> +static inline bool iommu_debug_pagealloc_enabled(void)
> +{
> +	return false;
> +}
> +
>  static inline void iommu_debug_map(struct iommu_domain *domain,
>  				   phys_addr_t phys, size_t size)
>  {
>  }
>  
> +static inline void iommu_debug_unmap_phys(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)
>  {
> -- 
> 2.43.5
>