drm/ttm: fix offset in VMAs with a pg_offs in ttm_bo_vm_access

VMAs with a pg_offs that's offset from the start of the vma_node need
to adjust the offset within the BO accordingly. This matches the
offset calculation in ttm_bo_vm_fault_reserved.
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Tested-by: Laurent Morichetti <laurent.morichetti@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/381169/

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -505,8 +505,10 @@ static int ttm_bo_vm_access_kmap(struct ttm_buffer_object *bo,
 int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
 		     void *buf, int len, int write)
 {
-	unsigned long offset = (addr) - vma->vm_start;
 	struct ttm_buffer_object *bo = vma->vm_private_data;
+	unsigned long offset = (addr) - vma->vm_start +
+		((vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node))
+		 << PAGE_SHIFT);
 	int ret;
 
 	if (len < 1 || (offset + len) >> PAGE_SHIFT > bo->num_pages)