On Wed, Oct 21, 2020 at 04:42:11PM +0200, Daniel Vetter wrote: > Uh yes. In drivers/gpu this isn't a problem because we only install > ptes from the vm_ops->fault handler. So no races. And I don't think > you can fix this otherwise through holding locks: mmap_sem we can't > hold because before vma_link we don't even know which mm_struct is > involved, so can't solve the race. Plus this would be worse that > mm_take_all_locks used by mmu notifier. And the address_space > i_mmap_lock is also no good since it's not held during the ->mmap > callback, when we write the ptes. And the resource locks is even less > useful, since we're not going to hold that at vma_link() time for > sure. > > Hence delaying the pte writes after the vma_link, which means ->fault > time, looks like the only way to close this gap. > Trouble is I have no idea how to do this cleanly ... How about add a vm_ops callback 'install_pages'/'prefault_pages' ? Call it after vm_link() - basically just move the remap_pfn, under some other lock, into there. Jason
