<html><head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head> <body> [SNIP] <blockquote type="cite" cite="mid:fc8f2af7-9fc2-cb55-3065-75a4060b7c82@amd.com"> But Jason pointed me to the right piece of code. See this comment in in mmap_region(): <blockquote type="cite"> <pre> /* ->mmap() can change vma->vm_file, but must guarantee that * vma_link() below can deny write-access if VM_DENYWRITE is set * and map writably if VM_SHARED is set. This usually means the * new file must not have been exposed to user-space, yet. */ <a href="https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/vma" moz-do-not-send="true">vma</a>-><a href="https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/vm_file" moz-do-not-send="true">vm_file</a> = <a href="https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/get_file" moz-do-not-send="true">get_file</a>(<a href="https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/file" moz-do-not-send="true">file</a>); error = <a href="https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/call_mmap" moz-do-not-send="true">call_mmap</a>(<a href="https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/file" moz-do-not-send="true">file</a>, <a href="https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/vma" moz-do-not-send="true">vma</a>);</pre> </blockquote> So changing vma->vm_file is allowed at least under certain circumstances. Only the "file must not have been exposed to user-space, yet" part still needs double checking. Currently working on that. </blockquote> Ok, I think we can guarantee for all DMA-bufs what is required here. While searching the code I've found that at least vgem_prime_mmap() and i915_gem_dmabuf_mmap() are doing the same thing of modifying vma->vm_file. So I'm leaning towards that this works as expected and we should just document this properly. Daniel and Jason what do you think? Christian. </body> </html>