[PATCH] drm/ttm: Don't inherit GEM object VMAs in child process

[Rajneesh Bhardwaj]

When an application having open file access to a node forks, its shared
mappings also get reflected in the address space of child process even
though it cannot access them with the object permissions applied. With the
existing permission checks on the gem objects, it might be reasonable to
also create the VMAs with VM_DONTCOPY flag so a user space application
doesn't need to explicitly call the madvise(addr, len, MADV_DONTFORK)
system call to prevent the pages in the mapped range to appear in the
address space of the child process. It also prevents the memory leaks
due to additional reference counts on the mapped BOs in the child
process that prevented freeing the memory in the parent for which we had
worked around earlier in the user space inside the thunk library.

Additionally, we faced this issue when using CRIU to checkpoint restore
an application that had such inherited mappings in the child which
confuse CRIU when it mmaps on restore. Having this flag set for the
render node VMAs helps. VMAs mapped via KFD already take care of this so
this is needed only for the render nodes.

Cc: Felix Kuehling <Felix.Kuehling at amd.com>

Signed-off-by: David Yat Sin <david.yatsin at amd.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj at amd.com>
---
 drivers/gpu/drm/drm_gem.c       | 3 ++-
 drivers/gpu/drm/ttm/ttm_bo_vm.c | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 09c820045859..d9c4149f36dd 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1058,7 +1058,8 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
 			goto err_drm_gem_object_put;
 		}
 
-		vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
+		vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND
+				| VM_DONTDUMP | VM_DONTCOPY;
 		vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
 		vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 	}
diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 33680c94127c..420a4898fdd2 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -566,7 +566,7 @@ int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
 
 	vma->vm_private_data = bo;
 
-	vma->vm_flags |= VM_PFNMAP;
+	vma->vm_flags |= VM_PFNMAP | VM_DONTCOPY;
 	vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
 	return 0;
 }
-- 
2.17.1