s390/pai: Fix missing PAI counter increments under heavy load

Machines with a larger number of CPUs and under heavy load sometimes
loose PAI counter increments during recording using events
-e CRYPTO_ÂLL or -e NNPA_ALL. Counting is not affected.
This happens when several PAI crypto counters are incremented during
the same cryptographic operation.

During schedule out the functions

paiXXX_sched_task() (with XXX either crypt or ext)
+--> pai_have_samples()
   +--> pai_have_sample()
	+--> pai_copy()
	+--> pai_push_sample()

are called to read out PAI counter values.
In pai_copy() the current values of PAI counters are read from the
PMU memory mapped page and compared to the values read during last
schedule out operation, which have been saved in a backup page
named PAI_SAVE_AREA(event). For each PAI counter a delta is calculated
and when the delta is positive, that PAI counter was incremented by
hardware. This positve delta is reported as raw data record attached
to a sample.
After all deltas have been calculated, the new PAI counter values
are saved in the backup page PAI_SAVE_AREA(event). However this is
done in pai_push_sample(), leaving a small window for missing hardware
triggered updates. Here is one scenario:

  PAI counter idx:   0   1   2   3   4   5   6   7  ....  N
                   +---+---+---+---+---+---+---+---+    +---+
  PAI counter page:|   |   | X |   |   |   |   |   |....| Y |
                   +---+---+---+---+---+---+---+---+    +---+

In pai_copy() each PAI counter value is read and compared
to its old value. This is done in a loop. When PAI counter indexed
N is read, the hardware might increment PAI counter indexed 2 again,
updating its value from X to X+1.
Later pai_push_sample() simply mem-copies the complete PAI counter
page to a backup page and the increment of X+1 is lost, because the
backup page now contains the new value.

Read each PAI counter and save this value in the backup page when
there is a positive delta. This omits any time window between read
and store. This also reduced the work load as only modified PAI
counters are saved.

Cc: stable@vger.kernel.org
Fixes: fe861b0c8d06 ("s390/pai: save PAI counter value page in event structure")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

1 files changed, 20 insertions, 9 deletions

diff --git a/arch/s390/kernel/perf_pai.c b/arch/s390/kernel/perf_pai.c
index f13c5c5fbea6..cdb8006220ca 100644
--- a/arch/s390/kernel/perf_pai.c
+++ b/arch/s390/kernel/perf_pai.c
@@ -186,6 +186,13 @@ static u64 pai_getctr(unsigned long *page, int nr, unsigned long offset)
 	return page[nr];
 }
 
+static void pai_setctr(unsigned long *page, int nr, unsigned long offset, u64 v)
+{
+	if (offset)
+		nr += offset / sizeof(*page);
+	page[nr] = v;
+}
+
 /* Read the counter values. Return value from location in CMP. For base
  * event xxx_ALL sum up all events. Returns counter value.
  */
@@ -551,6 +558,8 @@ static void paicrypt_del(struct perf_event *event, int flags)
 /* Create raw data and save it in buffer. Calculate the delta for each
  * counter between this invocation and the last invocation.
  * Returns number of bytes copied.
+ * After reading from PAI counter page, save the read value to the old
+ * page to calculate PAI counter deltas.
  * Saves only entries with positive counter difference of the form
  * 2 bytes: Number of counter
  * 8 bytes: Value of counter
@@ -562,16 +571,22 @@ static size_t pai_copy(struct pai_userdata *userdata, unsigned long *page,
 	int i, outidx = 0;
 
 	for (i = 1; i <= pp->num_avail; i++) {
-		u64 val = 0, val_old = 0;
+		u64 val = 0, val_old = 0, val_k = 0, val_old_k = 0;
 
 		if (!exclude_kernel) {
-			val += pai_getctr(page, i, pp->kernel_offset);
-			val_old += pai_getctr(page_old, i, pp->kernel_offset);
+			val_k = pai_getctr(page, i, pp->kernel_offset);
+			val_old_k = pai_getctr(page_old, i, pp->kernel_offset);
+			if (val_k != val_old_k)
+				pai_setctr(page_old, i, pp->kernel_offset, val_k);
 		}
 		if (!exclude_user) {
-			val += pai_getctr(page, i, 0);
-			val_old += pai_getctr(page_old, i, 0);
+			val = pai_getctr(page, i, 0);
+			val_old = pai_getctr(page_old, i, 0);
+			if (val != val_old)
+				pai_setctr(page_old, i, 0, val);
 		}
+		val += val_k;
+		val_old += val_old_k;
 		if (val >= val_old)
 			val -= val_old;
 		else
@@ -602,8 +617,6 @@ static size_t pai_copy(struct pai_userdata *userdata, unsigned long *page,
 static int pai_push_sample(size_t rawsize, struct pai_map *cpump,
 			   struct perf_event *event)
 {
-	int idx = PAI_PMU_IDX(event);
-	struct pai_pmu *pp = &pai_pmu[idx];
 	struct perf_sample_data data;
 	struct perf_raw_record raw;
 	struct pt_regs regs;
@@ -634,8 +647,6 @@ static int pai_push_sample(size_t rawsize, struct pai_map *cpump,
 
 	overflow = perf_event_overflow(event, &data, &regs);
 	perf_event_update_userpage(event);
-	/* Save crypto counter lowcore page after reading event data. */
-	memcpy((void *)PAI_SAVE_AREA(event), cpump->area, pp->area_size);
 	return overflow;
 }