On 03/26/23 10:46, Peter Xu wrote: > 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. > I am OK with separate patches, and agree that the R/O pinning case is less likely to happen. Since this patch addresses the issue found by Muhammad, Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> -- Mike Kravetz
