From d1751118c88673fe5a948ad82277898e9e284c55 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Wed, 4 Jan 2023 17:52:07 -0500 Subject: mm/uffd: detect pgtable allocation failures Before this patch, when there's any pgtable allocation issues happened during change_protection(), the error will be ignored from the syscall. For shmem, there will be an error dumped into the host dmesg. Two issues with that: (1) Doing a trace dump when allocation fails is not anything close to grace. (2) The user should be notified with any kind of such error, so the user can trap it and decide what to do next, either by retrying, or stop the process properly, or anything else. For userfault users, this will change the API of UFFDIO_WRITEPROTECT when pgtable allocation failure happened. It should not normally break anyone, though. If it breaks, then in good ways. One man-page update will be on the way to introduce the new -ENOMEM for UFFDIO_WRITEPROTECT. Not marking stable so we keep the old behavior on the 5.19-till-now kernels. [akpm@linux-foundation.org: coding-style cleanups] Link: https://lkml.kernel.org/r/20230104225207.1066932-4-peterx@redhat.com Signed-off-by: Peter Xu Reported-by: James Houghton Acked-by: James Houghton Cc: Andrea Arcangeli Cc: Axel Rasmussen Cc: David Hildenbrand Cc: Mike Kravetz Cc: Muchun Song Cc: Nadav Amit Signed-off-by: Andrew Morton --- mm/mempolicy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm/mempolicy.c') diff --git a/mm/mempolicy.c b/mm/mempolicy.c index a86b8f15e2f09..85a34f1f3ab8f 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -636,7 +636,7 @@ unsigned long change_prot_numa(struct vm_area_struct *vma, tlb_gather_mmu(&tlb, vma->vm_mm); nr_updated = change_protection(&tlb, vma, addr, end, MM_CP_PROT_NUMA); - if (nr_updated) + if (nr_updated > 0) count_vm_numa_events(NUMA_PTE_UPDATES, nr_updated); tlb_finish_mmu(&tlb); -- cgit 1.2.3-korg