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From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, almasrymina@google.com,
	axelrasmussen@google.com, linux-mm@kvack.org,
	mike.kravetz@oracle.com, mm-commits@vger.kernel.org,
	peterx@redhat.com, stable@vger.kernel.org,
	torvalds@linux-foundation.org
Subject: [patch 10/13] mm, hugetlb: fix simple resv_huge_pages underflow on UFFDIO_COPY
Date: Fri, 04 Jun 2021 20:01:36 -0700	[thread overview]
Message-ID: <20210605030136.4bhX4XMbm%akpm@linux-foundation.org> (raw)
In-Reply-To: <20210604200040.d8d0406caf195525620c0f3d@linux-foundation.org>

From: Mina Almasry <almasrymina@google.com>
Subject: mm, hugetlb: fix simple resv_huge_pages underflow on UFFDIO_COPY

The userfaultfd hugetlb tests cause a resv_huge_pages underflow. This
happens when hugetlb_mcopy_atomic_pte() is called with !is_continue on an
index for which we already have a page in the cache.  When this happens,
we allocate a second page, double consuming the reservation, and then fail
to insert the page into the cache and return -EEXIST.

To fix this, we first check if there is a page in the cache which already
consumed the reservation, and return -EEXIST immediately if so.

There is still a rare condition where we fail to copy the page contents
AND race with a call for hugetlb_no_page() for this index and again we
will underflow resv_huge_pages.  That is fixed in a more complicated patch
not targeted for -stable.

Test:
Hacked the code locally such that resv_huge_pages underflows produce
a warning, then:

./tools/testing/selftests/vm/userfaultfd hugetlb_shared 10
	2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success
./tools/testing/selftests/vm/userfaultfd hugetlb 10
	2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success

Both tests succeed and produce no warnings. After the
test runs number of free/resv hugepages is correct.

[mike.kravetz@oracle.com: changelog fixes]
Link: https://lkml.kernel.org/r/20210528004649.85298-1-almasrymina@google.com
Fixes: 8fb5debc5fcd ("userfaultfd: hugetlbfs: add hugetlb_mcopy_atomic_pte for userfaultfd support")
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-fix-simple-resv_huge_pages-underflow-on-uffdio_copy
+++ a/mm/hugetlb.c
@@ -4889,10 +4889,20 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 		if (!page)
 			goto out;
 	} else if (!*pagep) {
-		ret = -ENOMEM;
+		/* If a page already exists, then it's UFFDIO_COPY for
+		 * a non-missing case. Return -EEXIST.
+		 */
+		if (vm_shared &&
+		    hugetlbfs_pagecache_present(h, dst_vma, dst_addr)) {
+			ret = -EEXIST;
+			goto out;
+		}
+
 		page = alloc_huge_page(dst_vma, dst_addr, 0);
-		if (IS_ERR(page))
+		if (IS_ERR(page)) {
+			ret = -ENOMEM;
 			goto out;
+		}
 
 		ret = copy_huge_page_from_user(page,
 						(const void __user *) src_addr,
_


  parent reply	other threads:[~2021-06-05  6:07 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-05  3:00 incoming Andrew Morton
2021-06-05  3:01 ` [patch 01/13] Revert "MIPS: make userspace mapping young by default" Andrew Morton
2021-06-05  3:01 ` [patch 02/13] kfence: use TASK_IDLE when awaiting allocation Andrew Morton
2021-06-05  3:01 ` [patch 03/13] pid: take a reference when initializing `cad_pid` Andrew Morton
2021-06-05  3:01 ` [patch 04/13] mm/debug_vm_pgtable: fix alignment for pmd/pud_advanced_tests() Andrew Morton
2021-06-05  3:01 ` [patch 05/13] mm/page_alloc: fix counting of free pages after take off from buddy Andrew Morton
2021-06-05  3:01 ` [patch 06/13] drivers/base/memory: fix trying offlining memory blocks with memory holes on aarch64 Andrew Morton
2021-06-05  3:01 ` [patch 07/13] hugetlb: pass head page to remove_hugetlb_page() Andrew Morton
2021-06-05  3:01 ` [patch 08/13] proc: add .gitignore for proc-subset-pid selftest Andrew Morton
2021-06-05  3:01 ` [patch 09/13] mm/kasan/init.c: fix doc warning Andrew Morton
2021-06-05  3:01 ` Andrew Morton [this message]
2021-06-05  3:01 ` [patch 11/13] lib: crc64: fix kernel-doc warning Andrew Morton
2021-06-05  3:01 ` [patch 12/13] ocfs2: fix data corruption by fallocate Andrew Morton
2021-06-05  3:01 ` [patch 13/13] mailmap: use private address for Michel Lespinasse Andrew Morton

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