Re: [PATCH v2 4/4] drivers/iommu-debug-pagealloc: Check mapped/unmapped kernel memory

Mostafa Saleh
2025-11-24T12:38:56Z

On Thu, Nov 13, 2025 at 10:59:57AM +0000, Will Deacon wrote:
> On Thu, Nov 06, 2025 at 04:39:53PM +0000, Mostafa Saleh wrote:
> > Now, as the page_ext holds count of IOMMU mappings, we can use it to
> > assert that any page allocated/freed is indeed not in the IOMMU.
> >
> > The sanitizer doesn’t protect against mapping/unmapping during this
> > period. However, that’s less harmful as the page is not used by the
> > kernel.
> >
> > Signed-off-by: Mostafa Saleh <smostafa@google.com>
> > Tested-by: Qinxin Xia <xiaqinxin@huawei.com>
> > ---
> > drivers/iommu/iommu-debug-pagealloc.c | 19 +++++++++++++++++++
> > include/linux/iommu-debug-pagealloc.h | 12 ++++++++++++
> > include/linux/mm.h | 5 +++++
> > 3 files changed, 36 insertions(+)
> >
> > diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c
> > index 0e14104b971c..5b26c84d3a0e 100644
> > --- a/drivers/iommu/iommu-debug-pagealloc.c
> > +++ b/drivers/iommu/iommu-debug-pagealloc.c
> > @@ -71,6 +71,25 @@ static size_t iommu_debug_page_size(struct iommu_domain *domain)
> > return 1UL << __ffs(domain->pgsize_bitmap);
> > }
> >
> > +static unsigned int iommu_debug_page_count(unsigned long phys)
>
> 'phys_addr_t phys' ?
>
> But having said that, wouldn't you be better off taking the
> 'struct page *' here rather than converting it to a physical address
> only for get_iommu_page_ext() to convert it straight back again?

Will do, we will need the physical address anyway for the error message.

>
> > +{
> > + unsigned int ref;
> > + struct page_ext *page_ext = get_iommu_page_ext(phys);
> > + struct iommu_debug_metadate *d = get_iommu_data(page_ext);
> > +
> > + ref = atomic_read(&d->ref);
> > + page_ext_put(page_ext);
> > + return ref;
> > +}
> > +
> > +void __iommu_debug_check_unmapped(const struct page *page, int numpages)
> > +{
> > + while (numpages--) {
> > + WARN_ON(iommu_debug_page_count(page_to_phys(page)));
>
> Since you only care about the count being non-zero, perhaps tweak
> iommu_debug_page_count() to be something like:
>
> bool iommu_debug_page_referenced(struct page *);
>

Will do.

Thanks,
Mostafa

> Will