On Fri, Mar 24, 2023 at 11:36:53PM +0100, David Hildenbrand wrote: > > > @@ -5487,6 +5487,17 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma, > > > unsigned long haddr = address & huge_page_mask(h); > > > struct mmu_notifier_range range; > > > + /* > > > + * Never handle CoW for uffd-wp protected pages. It should be only > > > + * handled when the uffd-wp protection is removed. > > > + * > > > + * Note that only the CoW optimization path (in hugetlb_no_page()) > > > + * can trigger this, because hugetlb_fault() will always resolve > > > + * uffd-wp bit first. > > > + */ > > > + if (!unshare && huge_pte_uffd_wp(pte)) > > > + return 0; > > > > This looks correct. However, since the previous version looked correct I must > > ask. Can we have unshare set and huge_pte_uffd_wp true? If so, then it seems > > we would need to possibly propogate that uffd_wp to the new pte as in v2 Good point, thanks for spotting! > > We can. A reproducer would share an anon hugetlb page because parent and > child. In the parent, we would uffd-wp that page. We could trigger unsharing > by R/O-pinning that page. Right. This seems to be a separate bug.. It should be triggered in totally different context and much harder due to rare use of RO pins, meanwhile used with userfault-wp. If both of you agree, I can prepare a separate patch for this bug, and I'll better prepare a reproducer/selftest with it. -- Peter Xu
