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.