Re: [PATCH] drm/gpusvm,pagemap: Do not assume DRM pagemap owns device pages

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Apr 10, 2026 at 02:46:54PM +0200, Francois Dugast wrote:
> On Wed, Apr 08, 2026 at 06:55:12PM -0700, Matthew Brost wrote:
> > Update drm_pagemap_page_zone_device_data() to derive the pgmap ops from
> > the page and compare them against the DRM pagemap ops. If the ops do not
> > match, return NULL.
> > 
> > Also harden two risky call sites by checking for NULL after
> > hmm_range_fault() or migrate_vma_setup() when migrating to device
> > memory, as it is possible to encounter device pages that are not owned
> > by DRM pagemap.
> 
> Shouldn't we also harden other calls to drm_pagemap_page_zone_device_data() in
> 
>     drm_pagemap_migrate_map_device_private_pages()
>     drm_pagemap_migrate_unmap_pages()

We sanitize prior to this in drm_pagemap_migrate_to_devmem or are
operating on pages handed back via populate_devmem_pfn.

>     drm_pagemap_migrate_populate_ram_pfn()

Operating on page handed back via populate_devmem_pfn. Also wouldn't
NULL ptr reference.

>     __drm_pagemap_migrate_to_ram()
>     drm_pagemap_folio_free()
>     drm_pagemap_migrate_to_ram()

These are in the vops path of pagemap we check against.

>     drm_pagemap_page_to_dpagemap()

We sanitize prior to this in drm_gpusvm_get_pages.

Thus all the above sites I figure a warn is enough as it would indicate
a fairly serious bug in drm gpusvm/pagemap/calling driver which this
code completely controls.

The case where I do sanitize - after collection via hmm_range_fault,
migrate_vma_setup, I think it could be possible an outside driver has
moved pages to private (very unlikely) and this driver also tries to
move, so abort rather NULL ptr dereference.

So basically mitagated the 2 risky places with sanitization. Ofc we
could check this everywhere...

Matt

> 
> Francois
> 
> > 
> > Suggested-by: sashiko.dev
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> >  drivers/gpu/drm/drm_gpusvm.c  |  5 +++++
> >  drivers/gpu/drm/drm_pagemap.c | 14 ++++++++++----
> >  include/drm/drm_pagemap.h     |  5 ++++-
> >  3 files changed, 19 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> > index 365a9c0b522a..b3cccd047a21 100644
> > --- a/drivers/gpu/drm/drm_gpusvm.c
> > +++ b/drivers/gpu/drm/drm_gpusvm.c
> > @@ -1506,6 +1506,11 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
> >  			struct drm_pagemap_zdd *__zdd =
> >  				drm_pagemap_page_zone_device_data(page);
> >  
> > +			if (!__zdd) {
> > +				err = -EINVAL;
> > +				goto err_unmap;
> > +			}
> > +
> >  			if (!ctx->allow_mixed &&
> >  			    zdd != __zdd && i > 0) {
> >  				err = -EOPNOTSUPP;
> > diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> > index d82ea7ccb8da..95c951c5b569 100644
> > --- a/drivers/gpu/drm/drm_pagemap.c
> > +++ b/drivers/gpu/drm/drm_pagemap.c
> > @@ -753,10 +753,16 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
> >  				own_pages++;
> >  				goto next;
> >  			}
> > -			cur.dpagemap = src_zdd->dpagemap;
> > -			cur.ops = src_zdd->devmem_allocation->ops;
> > -			cur.device = cur.dpagemap->drm->dev;
> > -			pages[i] = src_page;
> > +			if (src_zdd) {
> > +				cur.dpagemap = src_zdd->dpagemap;
> > +				cur.ops = src_zdd->devmem_allocation->ops;
> > +				cur.device = cur.dpagemap->drm->dev;
> > +				pages[i] = src_page;
> > +			} else {
> > +				npages = i;
> > +				err = -EINVAL;
> > +				goto err_finalize;
> > +			}
> >  		}
> >  		if (!pages[i]) {
> >  			cur.dpagemap = NULL;
> > diff --git a/include/drm/drm_pagemap.h b/include/drm/drm_pagemap.h
> > index 95eb4b66b057..9b7c50932db5 100644
> > --- a/include/drm/drm_pagemap.h
> > +++ b/include/drm/drm_pagemap.h
> > @@ -367,12 +367,15 @@ int drm_pagemap_reinit(struct drm_pagemap *dpagemap);
> >   * drm_pagemap_page_zone_device_data() - Page to zone_device_data
> >   * @page: Pointer to the page
> >   *
> > - * Return: Page's zone_device_data
> > + * Return: Page's zone_device_data if owned by DRM pagemap, NULL otherwise
> >   */
> >  static inline struct drm_pagemap_zdd *drm_pagemap_page_zone_device_data(struct page *page)
> >  {
> >  	struct folio *folio = page_folio(page);
> >  
> > +	if (WARN_ON_ONCE(page_pgmap(page)->ops != drm_pagemap_pagemap_ops_get()))
> > +		return NULL;
> > +
> >  	return folio_zone_device_data(folio);
> >  }
> >  
> > -- 
> > 2.34.1
> >