On Wed, Jan 27, 2016 at 12:32:16PM -0800, Andy Lutomirski wrote: > On Wed, Jan 27, 2016 at 11:39 AM, Johannes Weiner <[email protected]> wrote: > > Could the VDSO be a VM_MIXEDMAP to keep the initial unmanaged pages > > out of the VM while allowing COW into regular anonymous pages? > > Probably. What are its limitations? We want ptrace to work on it, > and mprotect needs to work and allow COW. access_process_vm should > probably work, too.
Thanks, that's good to know. However, after looking at this a little longer, it appears this would need work in do_wp_page() to support non-page COW copying, then adding vm_ops->access and complicating ->fault in all VDSO implementations. And it looks like - at least theoretically - drivers can inject non-VM pages into the page tables as well (comment above insert_page()) Given that this behavior has been around for a long time (the comment at the bottom of vm_normal_page is ancient), I'll probably go with a more conservative approach; add a comment to mark_page_accessed() and filter out non-VM pages in the function I'm going to call from it. Thanks!
