[PATCH net] net: mana: Fix race on per-CQ variable napi work_done

[Haiyang Zhang <haiyangz@microsoft.com>]

After calling napi_complete_done(), the NAPIF_STATE_SCHED bit may be
cleared, and another CPU can start napi thread and access per-CQ variable,
cq->work_done. If the other thread (for example, from busy_poll) sets
it to a value >= budget, this thread will continue to run when it should
stop, and cause memory corruption and panic.

To fix this issue, save the per-CQ work_done variable in a local variable
before napi_complete_done(), so it won't be corrupted by a possible
concurrent thread after napi_complete_done().

Also, add a flag bit to advertise to the NIC firmware: the NAPI work_done
variable race is fixed, so the driver is able to reliably support features
like busy_poll.

Cc: stable@vger.kernel.org
Fixes: e1b5683ff62e ("net: mana: Move NAPI from EQ to CQ")
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
---
 drivers/net/ethernet/microsoft/mana/gdma.h    |  9 ++++++++-
 drivers/net/ethernet/microsoft/mana/mana_en.c | 16 +++++++++++-----
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/microsoft/mana/gdma.h b/drivers/net/ethernet/microsoft/mana/gdma.h
index 4a6efe6ada08..65c24ee49efd 100644
--- a/drivers/net/ethernet/microsoft/mana/gdma.h
+++ b/drivers/net/ethernet/microsoft/mana/gdma.h
@@ -498,7 +498,14 @@ enum {
 
 #define GDMA_DRV_CAP_FLAG_1_EQ_SHARING_MULTI_VPORT BIT(0)
 
-#define GDMA_DRV_CAP_FLAGS1 GDMA_DRV_CAP_FLAG_1_EQ_SHARING_MULTI_VPORT
+/* Advertise to the NIC firmware: the NAPI work_done variable race is fixed,
+ * so the driver is able to reliably support features like busy_poll.
+ */
+#define GDMA_DRV_CAP_FLAG_1_NAPI_WKDONE_FIX BIT(2)
+
+#define GDMA_DRV_CAP_FLAGS1 \
+	(GDMA_DRV_CAP_FLAG_1_EQ_SHARING_MULTI_VPORT | \
+	 GDMA_DRV_CAP_FLAG_1_NAPI_WKDONE_FIX)
 
 #define GDMA_DRV_CAP_FLAGS2 0
 
diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index 9259a74eca40..27a0f3af8aab 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -1303,10 +1303,11 @@ static void mana_poll_rx_cq(struct mana_cq *cq)
 		xdp_do_flush();
 }
 
-static void mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
+static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
 {
 	struct mana_cq *cq = context;
 	u8 arm_bit;
+	int w;
 
 	WARN_ON_ONCE(cq->gdma_cq != gdma_queue);
 
@@ -1315,26 +1316,31 @@ static void mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
 	else
 		mana_poll_tx_cq(cq);
 
-	if (cq->work_done < cq->budget &&
-	    napi_complete_done(&cq->napi, cq->work_done)) {
+	w = cq->work_done;
+
+	if (w < cq->budget &&
+	    napi_complete_done(&cq->napi, w)) {
 		arm_bit = SET_ARM_BIT;
 	} else {
 		arm_bit = 0;
 	}
 
 	mana_gd_ring_cq(gdma_queue, arm_bit);
+
+	return w;
 }
 
 static int mana_poll(struct napi_struct *napi, int budget)
 {
 	struct mana_cq *cq = container_of(napi, struct mana_cq, napi);
+	int w;
 
 	cq->work_done = 0;
 	cq->budget = budget;
 
-	mana_cq_handler(cq, cq->gdma_cq);
+	w = mana_cq_handler(cq, cq->gdma_cq);
 
-	return min(cq->work_done, budget);
+	return min(w, budget);
 }
 
 static void mana_schedule_napi(void *context, struct gdma_queue *gdma_queue)
-- 
2.25.1