Are MMU notifiers not handling copy-on-write of hugetlb pages?
Looking at the source code, I don't see where this happens.
Non-hugetlb pages are handled via:
do_wp_page() -> set_pte_at_notify() -> mmu_notifier_change_pte()
...but I don't see any MMU notifier callouts down the hugetlb_cow() path,
unless it fails to allocate a new_page():
new_page = alloc_huge_page(vma, address, outside_reserve);
if (IS_ERR(new_page)) {
page_cache_release(old_page);
/*
* If a process owning a MAP_PRIVATE mapping fails to COW,
* it is due to references held by a child and an insufficient
* huge page pool. To guarantee the original mappers
* reliability, unmap the page from child processes. The child
* may get SIGKILLed if it later faults.
*/
if (outside_reserve) {
BUG_ON(huge_pte_none(pte));
>>> if (unmap_ref_private(mm, vma, old_page, address)) {
..where unmap_ref_private() calls __unmap_hugepage_range() which then
calls the MMU notifier invalidate_range functions.
Am I missing something?
Thanks,
Dean
--
Dean Roe
Cray Inc.
roe@xxxxxxxx
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