On Fri, Oct 22, 2021 at 8:06 AM Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > Probing only the first byte(s) in fault_in() would be ideal, no need to > go through all filesystems and try to change the uaccess/probing order. Let's try that. Or rather: probing just the first page - since there are users like that btrfs ioctl, and the direct-io path. Linus