pds_core: order completion reads after the ownership check

[ Upstream commit dd6b1cc ]

pdsc_process_adminq() and pdsc_process_notifyq() decide a completion is
valid from its ownership field - the color bit for the adminq, the event
id for the notifyq - then read the rest of the descriptor, with no
barrier in between.

On a weakly ordered architecture the CPU may read the payload first. Add
dma_rmb() between the ownership read and the payload reads.

Fixes: 7e82a87 ("pds_core: Prevent race issues involving the adminq")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260629200358.2626129-1-nikhil.rao%40amd.com?part=2
Signed-off-by: Nikhil P. Rao <nikhil.rao@amd.com>
Reviewed-by: Eric Joyner <eric.joyner@amd.com>
Link: https://patch.msgid.link/20260714204145.1782390-1-nikhil.rao@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: nprao1

drivers/net/ethernet/amd/pds_core/adminq.c

@@ -18,7 +18,13 @@ static int pdsc_process_notifyq(struct pdsc_qcq *qcq)
 	comp = cq_info->comp;
 	eid = le64_to_cpu(comp->event.eid);
 	while (eid > pdsc->last_eid) {
-		u16 ecode = le16_to_cpu(comp->event.ecode);
+		u16 ecode;
+
+		/* Order the payload read after the event id, the field the
+		 * driver uses to detect a new completion.
+		 */
+		dma_rmb();
+		ecode = le16_to_cpu(comp->event.ecode);
 
 		switch (ecode) {
 		case PDS_EVENT_LINK_CHANGE:
@@ -102,6 +108,10 @@ void pdsc_process_adminq(struct pdsc_qcq *qcq)
 	spin_lock_irqsave(&pdsc->adminq_lock, irqflags);
 	comp = cq->info[cq->tail_idx].comp;
 	while (pdsc_color_match(comp->color, cq->done_color)) {
+		/* Order the payload reads after the color bit, the field the
+		 * driver uses to detect a new completion.
+		 */
+		dma_rmb();
 		q_info = &q->info[q->tail_idx];
 		q->tail_idx = (q->tail_idx + 1) & (q->num_descs - 1);