selftests/powerpc: Relax L1d miss targets for rfi_flush test

When running the rfi_flush test, if the system is loaded, we see two
issues:
1. The L1d misses when rfi_flush is disabled increase significantly due
to other workloads interfering with the cache.
2. The L1d misses when rfi_flush is enabled sometimes goes slightly
below the expected number of misses.

To address these, let's relax the expected number of L1d misses:
1. When rfi_flush is disabled, we allow upto half the expected number of
the misses for when rfi_flush is enabled.
2. When rfi_flush is enabled, we allow ~1% lower number of cache misses.

Reported-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Tested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 13 insertions, 5 deletions

diff --git a/tools/testing/selftests/powerpc/security/rfi_flush.c b/tools/testing/selftests/powerpc/security/rfi_flush.c
index 564ed45bbf73..0a7d0afb26b8 100644
--- a/tools/testing/selftests/powerpc/security/rfi_flush.c
+++ b/tools/testing/selftests/powerpc/security/rfi_flush.c
@@ -49,6 +49,7 @@ int rfi_flush_test(void)
         struct perf_event_read v;
         __u64 l1d_misses_total = 0;
         unsigned long iterations = 100000, zero_size = 24 * 1024;
+        unsigned long l1d_misses_expected;
         int rfi_flush_org, rfi_flush;
 
         SKIP_IF(geteuid() != 0);
@@ -71,6 +72,12 @@ int rfi_flush_test(void)
 
         iter = repetitions;
 
+        /*
+         * We expect to see l1d miss for each cacheline access when rfi_flush
+         * is set. Allow a small variation on this.
+         */
+        l1d_misses_expected = iterations * (zero_size / CACHELINE_SIZE - 2);
+
 again:
         FAIL_IF(perf_event_reset(fd));
 
@@ -78,10 +85,9 @@ again:
 
         FAIL_IF(read(fd, &v, sizeof(v)) != sizeof(v));
 
-        /* Expect at least zero_size/CACHELINE_SIZE misses per iteration */
-        if (v.l1d_misses >= (iterations * zero_size / CACHELINE_SIZE) && rfi_flush)
+        if (rfi_flush && v.l1d_misses >= l1d_misses_expected)
                 passes++;
-        else if (v.l1d_misses < iterations && !rfi_flush)
+        else if (!rfi_flush && v.l1d_misses < (l1d_misses_expected / 2))
                 passes++;
 
         l1d_misses_total += v.l1d_misses;
@@ -92,13 +98,15 @@ again:
         if (passes < repetitions) {
                 printf("FAIL (L1D misses with rfi_flush=%d: %llu %c %lu) [%d/%d failures]\n",
                        rfi_flush, l1d_misses_total, rfi_flush ? '<' : '>',
-                       rfi_flush ? (repetitions * iterations * zero_size / CACHELINE_SIZE) : iterations,
+                       rfi_flush ? repetitions * l1d_misses_expected :
+                       repetitions * l1d_misses_expected / 2,
                        repetitions - passes, repetitions);
                 rc = 1;
         } else
                 printf("PASS (L1D misses with rfi_flush=%d: %llu %c %lu) [%d/%d pass]\n",
                        rfi_flush, l1d_misses_total, rfi_flush ? '>' : '<',
-                       rfi_flush ? (repetitions * iterations * zero_size / CACHELINE_SIZE) : iterations,
+                       rfi_flush ? repetitions * l1d_misses_expected :
+                       repetitions * l1d_misses_expected / 2,
                        passes, repetitions);
 
         if (rfi_flush == rfi_flush_org) {