On Thu, Sep 14, 2023 at 2:57 PM Nadav Amit <nadav.amit@xxxxxxxxx> wrote: > > > > On Sep 14, 2023, at 8:26 AM, Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > > > + if (!pte_same(ptep_clear_flush(src_vma, src_addr, src_pte), > > + orig_src_pte)) > > + BUG_ON(1); > > Just a minor detail regarding these few lines: > > Besides the less-than-ideal use of BUG_ON() here, I think that this code > assumes that the PTE cannot change at this point. However, as the PTE was > still mapped at this point, I think the access and dirty bits can be set. At this point we are holding PTLs for both PTEs (see double_pt_lock()). Can a PTE be modified from under us in this situation? > > tl;dr: this appears to be triggerable by userspace. > > [ as for the performance of this code, the lack of batching would mean > that for multithreaded applications where more than a single page is > remapped, performance would suffer ] Thanks for the note! I'll see if it's possible to implement some batching mechanism here. Thanks, Suren.
