On Thu, 30 Jan 2020 18:23:41 +0200 Mike Rapoport <rppt@xxxxxxxxxx> wrote: > Hi, > > This is essentially a resend of my attempt to implement "secret" mappings > using a file descriptor [1]. So one little thing I was curious about as I read through the patch... > +static int secretmem_check_limits(struct vm_fault *vmf) > +{ > + struct secretmem_state *state = vmf->vma->vm_file->private_data; > + struct inode *inode = file_inode(vmf->vma->vm_file); > + unsigned long limit; > + > + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) > + return -EINVAL; > + > + limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT; > + if (state->nr_pages + 1 >= limit) > + return -EPERM; > + > + return 0; > +} If I'm not mistaken, this means each memfd can be RLIMIT_MEMLOCK in length, with no global limit on the number of locked pages. What's keeping me from creating 1000 of these things and locking down lots of RAM? Thanks, jon