Commit cb2a2a5b authored by Boris Brezillon's avatar Boris Brezillon
Browse files

drm/shmem_helper: Make sure PMD entries get the writeable upgrade 



Unlike PTEs which are automatically upgraded to writeable entries if
.pfn_mkwrite() returns 0, the PMD upgrades go through .huge_fault(),
and we currently pretend to have handled the make-writeable request
even though we only ever map things read-only. Make sure we pass the
proper "write" info to vmf_insert_pfn_pmd() in that case.

This also means we have to record the mkwrite event in the .huge_fault()
path now. Move the dirty tracking logic to a
drm_gem_shmem_record_mkwrite() helper so it can also be called from
drm_gem_shmem_pfn_mkwrite().

Note that this wasn't a problem before commit 28e39181
("drm/gem-shmem: Track folio accessed/dirty status in mmap"), because
the pgprot were not lowered to read-only before this commit (see the
vma_wants_writenotify() in vma_set_page_prot()).

Fixes: 28e39181 ("drm/gem-shmem: Track folio accessed/dirty status in mmap")
Cc: Biju Das <biju.das.jz@bp.renesas.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Reviewed-by: default avatarLoïc Molinari <loic.molinari@collabora.com>
Tested-by: default avatarBiju Das <biju.das.jz@bp.renesas.com>
Acked-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Tested-by: default avatarTommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Link: https://patch.msgid.link/20260320151914.586945-1-boris.brezillon@collabora.com


Signed-off-by: default avatarBoris Brezillon <boris.brezillon@collabora.com>
parent c636ae34

drivers/gpu/drm/drm_gem_shmem_helper.c

+32 −14
Original line number Diff line number Diff line
@@ -554,6 +554,21 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev, 
}

EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create);



static void drm_gem_shmem_record_mkwrite(struct vm_fault *vmf)

{

	struct vm_area_struct *vma = vmf->vma;

	struct drm_gem_object *obj = vma->vm_private_data;

	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

	loff_t num_pages = obj->size >> PAGE_SHIFT;

	pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within VMA */



	if (drm_WARN_ON(obj->dev, !shmem->pages || page_offset >= num_pages))

		return;



	file_update_time(vma->vm_file);

	folio_mark_dirty(page_folio(shmem->pages[page_offset]));

}



static vm_fault_t try_insert_pfn(struct vm_fault *vmf, unsigned int order,

				 unsigned long pfn)

{
@@ -566,8 +581,23 @@ static vm_fault_t try_insert_pfn(struct vm_fault *vmf, unsigned int order, 


		if (aligned &&

		    folio_test_pmd_mappable(page_folio(pfn_to_page(pfn)))) {

			vm_fault_t ret;



			pfn &= PMD_MASK >> PAGE_SHIFT;

			return vmf_insert_pfn_pmd(vmf, pfn, false);



			/* Unlike PTEs which are automatically upgraded to

			 * writeable entries, the PMD upgrades go through

			 * .huge_fault(). Make sure we pass the "write" info

			 * along in that case.

			 * This also means we have to record the write fault

			 * here, instead of in .pfn_mkwrite().

			 */

			ret = vmf_insert_pfn_pmd(vmf, pfn,

						 vmf->flags & FAULT_FLAG_WRITE);

			if (ret == VM_FAULT_NOPAGE && (vmf->flags & FAULT_FLAG_WRITE))

				drm_gem_shmem_record_mkwrite(vmf);



			return ret;

		}

#endif

	}
@@ -655,19 +685,7 @@ static void drm_gem_shmem_vm_close(struct vm_area_struct *vma) 


static vm_fault_t drm_gem_shmem_pfn_mkwrite(struct vm_fault *vmf)

{

	struct vm_area_struct *vma = vmf->vma;

	struct drm_gem_object *obj = vma->vm_private_data;

	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

	loff_t num_pages = obj->size >> PAGE_SHIFT;

	pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within VMA */



	if (drm_WARN_ON(obj->dev, !shmem->pages || page_offset >= num_pages))

		return VM_FAULT_SIGBUS;



	file_update_time(vma->vm_file);



	folio_mark_dirty(page_folio(shmem->pages[page_offset]));



	drm_gem_shmem_record_mkwrite(vmf);

	return 0;

}