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Subject[PATCH 6/9] x86, pkeys, selftests: fix pkey exhaustion test off-by-one
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From: Dave Hansen <dave.hansen@linux.intel.com>

In our "exhaust all pkeys" test, we make sure that there
is the expected number available. Turns out that the
test did not cover the execute-only key, but discussed
it anyway. It did *not* discuss the test-allocated
key.

Now that we have a test for the mprotect(PROT_EXEC) case,
this off-by-one issue showed itself. Correct the off-by-
one and add the explanation for the case we missed.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Michael Ellermen <mpe@ellerman.id.au>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Shuah Khan <shuah@kernel.org>
---

b/tools/testing/selftests/x86/protection_keys.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff -puN tools/testing/selftests/x86/protection_keys.c~pkeys-selftests-exhaust-off-by-one tools/testing/selftests/x86/protection_keys.c
--- a/tools/testing/selftests/x86/protection_keys.c~pkeys-selftests-exhaust-off-by-one 2018-03-21 15:47:50.910198920 -0700
+++ b/tools/testing/selftests/x86/protection_keys.c 2018-03-21 15:47:50.914198920 -0700
@@ -1155,12 +1155,15 @@ void test_pkey_alloc_exhaust(int *ptr, u
pkey_assert(i < NR_PKEYS*2);

/*
- * There are 16 pkeys supported in hardware. One is taken
- * up for the default (0) and another can be taken up by
- * an execute-only mapping. Ensure that we can allocate
- * at least 14 (16-2).
+ * There are 16 pkeys supported in hardware. Three are
+ * allocated by the time we get here:
+ * 1. The default key (0)
+ * 2. One possibly consumed by an execute-only mapping.
+ * 3. One allocated by the test code and passed in via
+ * 'pkey' to this function.
+ * Ensure that we can allocate at least another 13 (16-3).
*/
- pkey_assert(i >= NR_PKEYS-2);
+ pkey_assert(i >= NR_PKEYS-3);

for (i = 0; i < nr_allocated_pkeys; i++) {
err = sys_pkey_free(allocated_pkeys[i]);
_
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