+ userfaultfd-support-minor-fault-handling-for-shmem-fix-4.patch added to -mm tree

+ userfaultfd-support-minor-fault-handling-for-shmem-fix-4.patch added to -mm tree

[akpm]

The patch titled
     Subject: userfaultfd/shmem: fix MCOPY_ATOMIC_CONTINUE behavior
has been added to the -mm tree.  Its filename is
     userfaultfd-support-minor-fault-handling-for-shmem-fix-4.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-support-minor-fault-handling-for-shmem-fix-4.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-support-minor-fault-handling-for-shmem-fix-4.patch

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------------------------------------------------------
From: Axel Rasmussen <axelrasmussen@google.com>
Subject: userfaultfd/shmem: fix MCOPY_ATOMIC_CONTINUE behavior

- Added back the userfaultfd.c selftest changes from v3; this file was
  mistakenly reverted in v4.

Link: https://lkml.kernel.org/r/20210405171917.2423068-1-axelrasmussen@google.com
Fixes: 00da60b9d0a0 ("userfaultfd: support minor fault handling for shmem")
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/vm/userfaultfd.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/tools/testing/selftests/vm/userfaultfd.c~userfaultfd-support-minor-fault-handling-for-shmem-fix-4
+++ a/tools/testing/selftests/vm/userfaultfd.c
@@ -368,11 +368,24 @@ static void wp_range(int ufd, __u64 star
 			(uint64_t)start);
 		exit(1);
 	}
+
+	/*
+	 * Error handling within the kernel for continue is subtly different
+	 * from copy or zeropage, so it may be a source of bugs. Trigger an
+	 * error (-EEXIST) on purpose, to verify doing so doesn't cause a BUG.
+	 */
+	req.mapped = 0;
+	ret = ioctl(ufd, UFFDIO_CONTINUE, &req);
+	if (ret >= 0 || req.mapped != -EEXIST) {
+		fprintf(stderr, "failed to exercise UFFDIO_CONTINUE error handling, ret=%d, mapped=%" PRId64, ret, req.mapped);
+		exit(1);
+	}
 }
 
 static void continue_range(int ufd, __u64 start, __u64 len)
 {
 	struct uffdio_continue req;
+	int ret;
 
 	req.range.start = start;
 	req.range.len = len;
_

Patches currently in -mm which might be from axelrasmussen@google.com are

userfaultfd-add-minor-fault-registration-mode.patch
userfaultfd-disable-huge-pmd-sharing-for-minor-registered-vmas.patch
userfaultfd-hugetlbfs-only-compile-uffd-helpers-if-config-enabled.patch
userfaultfd-add-uffdio_continue-ioctl.patch
userfaultfd-update-documentation-to-describe-minor-fault-handling.patch
userfaultfd-selftests-add-test-exercising-minor-fault-handling.patch
userfaultfd-support-minor-fault-handling-for-shmem.patch
userfaultfd-support-minor-fault-handling-for-shmem-fix.patch
userfaultfd-support-minor-fault-handling-for-shmem-fix-2.patch
userfaultfd-support-minor-fault-handling-for-shmem-fix-3.patch
userfaultfd-support-minor-fault-handling-for-shmem-fix-4.patch
userfaultfd-selftests-use-memfd_create-for-shmem-test-type.patch
userfaultfd-selftests-create-alias-mappings-in-the-shmem-test.patch
userfaultfd-selftests-reinitialize-test-context-in-each-test.patch
userfaultfd-selftests-exercise-minor-fault-handling-shmem-support.patch