From 8a13897fb0daa8f56821f263f0c63661e1c6acae Mon Sep 17 00:00:00 2001
From: Axel Rasmussen <axelrasmussen@google.com>
Date: Fri, 7 Jul 2023 14:55:37 -0700
Subject: [PATCH] mm: userfaultfd: support UFFDIO_POISON for hugetlbfs

The behavior here is the same as it is for anon/shmem.  This is done
separately because hugetlb pte marker handling is a bit different.

Link: https://lkml.kernel.org/r/20230707215540.2324998-6-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nadav Amit <namit@vmware.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/hugetlb.c     | 19 +++++++++++++++++++
 mm/userfaultfd.c |  3 +--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ffee2978dfed..7b076eb07a29 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6262,6 +6262,25 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 	int writable;
 	bool folio_in_pagecache = false;
 
+	if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {
+		ptl = huge_pte_lock(h, dst_mm, dst_pte);
+
+		/* Don't overwrite any existing PTEs (even markers) */
+		if (!huge_pte_none(huge_ptep_get(dst_pte))) {
+			spin_unlock(ptl);
+			return -EEXIST;
+		}
+
+		_dst_pte = make_pte_marker(PTE_MARKER_POISONED);
+		set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
+
+		/* No need to invalidate - it was non-present before */
+		update_mmu_cache(dst_vma, dst_addr, dst_pte);
+
+		spin_unlock(ptl);
+		return 0;
+	}
+
 	if (is_continue) {
 		ret = -EFAULT;
 		folio = filemap_lock_folio(mapping, idx);
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index dd167184575e..0fc69efa4f1f 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -377,8 +377,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
 	 * by THP.  Since we can not reliably insert a zero page, this
 	 * feature is not supported.
 	 */
-	if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE) ||
-	    uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {
+	if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
 		mmap_read_unlock(dst_mm);
 		return -EINVAL;
 	}