Re: [PATCH v3 2/4] drivers/iommu: Add calls for IOMMU_DEBUG_PAGEALLOC

[Mostafa Saleh <smostafa@google.com>]

On Tue, Nov 25, 2025 at 10:01 AM Mostafa Saleh <smostafa@google.com> wrote:
>
> On Tue, Nov 25, 2025 at 03:35:08PM +0800, Baolu Lu wrote:
> > 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@google.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
>
> My bad, I will fix it.
>
> >
> > [...]
> > > 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.
>
> It seemed better to have all the feature functions/declarations in one
> isolated file, as it is included outside of the iommu susbsystem also.
> I have no strong opinion, I can keep them in drivers/iommu/iommu-priv.h
> if you think it's better. But then we will have to include also
> "iommu-debug-pagealloc.h" for the static key to avoid including extra
> files to linux/mm.h.
>
> Thanks,
> Mostafa
>

Hi Baolu,

I plan to post a new version soon. So far, I only have the commit
subject rewrites. Do you have any opinion on the header file split or
the unmap size part?

Thanks,
Mostafa

> >
> > > +
> > >   #endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */
> > >   #endif /* __LINUX_IOMMU_DEBUG_PAGEALLOC_H */
> >
> > Thanks,
> > baolu