On Thu, Jan 31, 2019 at 01:37:03PM -0500, Jerome Glisse wrote: > @@ -207,8 +207,7 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, > > flush_cache_page(vma, addr, pte_pfn(*pvmw.pte)); > ptep_clear_flush_notify(vma, addr, pvmw.pte); > - set_pte_at_notify(mm, addr, pvmw.pte, > - mk_pte(new_page, vma->vm_page_prot)); > + set_pte_at(mm, addr, pvmw.pte, mk_pte(new_page, vma->vm_page_prot)); > > page_remove_rmap(old_page, false); > if (!page_mapped(old_page)) This seems racy by design in the way it copies the page, if the vma mapping isn't readonly to begin with (in which case it'd be ok to change the pfn with change_pte too, it'd be a from read-only to read-only change which is ok). If the code copies a writable page there's no much issue if coherency is lost by other means too. Said that this isn't a worthwhile optimization for uprobes so because of the lack of explicit read-only enforcement, I agree it's simpler to skip change_pte above. It's orthogonal, but in this function the mmu_notifier_invalidate_range_end(&range); can be optimized to mmu_notifier_invalidate_range_only_end(&range); otherwise there's no point to retain the _notify in ptep_clear_flush_notify.
