The PHC read path in ena_com_phc_get_timestamp() polls the shared
error_bound and timestamp fields for a matching req_id to detect
that the device has published a fresh reading. Both completion
checks read the payload without a barrier after observing req_id.
On weakly-ordered architectures the CPU may load the payload fields
before the req_id load is observed as updated, so a stale timestamp
or error bound can be returned while the read is reported as valid.
Add dma_rmb() after both req_id completion checks to order the
req_id load against the subsequent payload loads.
Fixes: a14be4dd8693 ("net/ena/base: add PHC error statistics")
Cc: [email protected]
Signed-off-by: Shai Brandes <[email protected]>
---
drivers/net/ena/base/ena_com.c | 50 +++++++++++++++++++++-------------
1 file changed, 31 insertions(+), 19 deletions(-)
diff --git a/drivers/net/ena/base/ena_com.c b/drivers/net/ena/base/ena_com.c
index f5b3cd70c8..f08d9214aa 100644
--- a/drivers/net/ena/base/ena_com.c
+++ b/drivers/net/ena/base/ena_com.c
@@ -2037,27 +2037,34 @@ int ena_com_phc_get_timestamp(struct ena_com_dev
*ena_dev, u64 *timestamp)
"PHC get time request 0x%x failed (device
error)\n",
phc->req_id);
phc->stats.phc_err_dv++;
- } else if (resp->error_flags & ENA_PHC_ERROR_FLAGS) {
- /* Device updated req_id during blocking time but got
- * a PHC error, this occurs if device:
- * - exceeded the get time request limit
- * - received an invalid timestamp
- * - received an excessively high error bound
- * - received an invalid error bound
- */
- ena_trc_err(ena_dev,
- "PHC get time request 0x%x failed (error
0x%x)\n",
- phc->req_id,
- resp->error_flags);
- phc->stats.phc_err_ts += !!(resp->error_flags &
- ENA_ADMIN_PHC_ERROR_FLAG_TIMESTAMP);
- phc->stats.phc_err_eb += !!(resp->error_flags &
- ENA_ADMIN_PHC_ERROR_FLAG_ERROR_BOUND);
} else {
- /* Device updated req_id during blocking time
- * with valid timestamp and error bound
+ /* Ensure PHC payload is read after req_id update
+ * is observed
*/
- phc->stats.phc_exp++;
+ dma_rmb();
+
+ if (resp->error_flags & ENA_PHC_ERROR_FLAGS) {
+ /* Device updated req_id during blocking time
+ * but got a PHC error, this occurs if device:
+ * - exceeded the get time request limit
+ * - received an invalid timestamp
+ * - received an excessively high error bound
+ * - received an invalid error bound
+ */
+ ena_trc_err(ena_dev,
+ "PHC get time request 0x%x failed
(error 0x%x)\n",
+ phc->req_id,
+ resp->error_flags);
+ phc->stats.phc_err_ts += !!(resp->error_flags &
+ ENA_ADMIN_PHC_ERROR_FLAG_TIMESTAMP);
+ phc->stats.phc_err_eb += !!(resp->error_flags &
+ ENA_ADMIN_PHC_ERROR_FLAG_ERROR_BOUND);
+ } else {
+ /* Device updated req_id during blocking time
+ * with valid timestamp and error bound
+ */
+ phc->stats.phc_exp++;
+ }
}
}
@@ -2100,6 +2107,11 @@ int ena_com_phc_get_timestamp(struct ena_com_dev
*ena_dev, u64 *timestamp)
continue;
}
+ /* Ensure PHC payload (timestamp, error_bound, error_flags)
+ * is read after req_id update is observed
+ */
+ dma_rmb();
+
/* req_id was updated by the device which indicates that
* PHC timestamp, error_bound and error_flags are updated too,
* checking errors before retrieving timestamp and
--
2.17.1
