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

[Mostafa Saleh]

On Thu, Aug 27, 2026 at 5:13 PM Mostafa Saleh <smostafa@xxxxxxxxxx> wrote:
>
> 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?
>

Ok I am missing that it might not be possible to call in the table
(iova_to_phys) while it is being freed.

> 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@xxxxxxxxxxxxxxxxx>
> > ---
> > 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
> >