sfc: Avoid generating over-length MC_CMD_FLUSH_RX_QUEUES request

MCDI supports requests up to 252 bytes long, which is only enough to
pass 63 RX queue IDs to MC_CMD_FLUSH_RX_QUEUES.  However a VF may have
up to 64 RX queues, and if we try to flush them all we will generate
an over-length request and BUG() in efx_mcdi_copyin().  Currently
all VF drivers limit themselves to 32 RX queues, so reducing the
limit to 63 does no harm.

Also add a BUILD_BUG_ON in efx_mcdi_flush_rxqs() so we remember to
deal with the same problem there if EFX_MAX_CHANNELS is increased.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/mcdi.c

@@ -1195,6 +1195,9 @@ int efx_mcdi_flush_rxqs(struct efx_nic *efx)
 	__le32 *qid;
 	int rc, count;
 
+	BUILD_BUG_ON(EFX_MAX_CHANNELS >
+		     MC_CMD_FLUSH_RX_QUEUES_IN_QID_OFST_MAXNUM);
+
 	qid = kmalloc(EFX_MAX_CHANNELS * sizeof(*qid), GFP_KERNEL);
 	if (qid == NULL)
 		return -ENOMEM;

drivers/net/ethernet/sfc/siena_sriov.c

@@ -21,6 +21,9 @@
 /* Number of longs required to track all the VIs in a VF */
 #define VI_MASK_LENGTH BITS_TO_LONGS(1 << EFX_VI_SCALE_MAX)
 
+/* Maximum number of RX queues supported */
+#define VF_MAX_RX_QUEUES 63
+
 /**
  * enum efx_vf_tx_filter_mode - TX MAC filtering behaviour
  * @VF_TX_FILTER_OFF: Disabled
@@ -578,6 +581,7 @@ static int efx_vfdi_init_rxq(struct efx_vf *vf)
 	efx_oword_t reg;
 
 	if (bad_vf_index(efx, vf_evq) || bad_vf_index(efx, vf_rxq) ||
+	    vf_rxq >= VF_MAX_RX_QUEUES ||
 	    bad_buf_count(buf_count, EFX_MAX_DMAQ_SIZE)) {
 		if (net_ratelimit())
 			netif_err(efx, hw, efx->net_dev,
@@ -683,6 +687,9 @@ static int efx_vfdi_fini_all_queues(struct efx_vf *vf)
 	__le32 *rxqs;
 	int rc;
 
+	BUILD_BUG_ON(VF_MAX_RX_QUEUES >
+		     MC_CMD_FLUSH_RX_QUEUES_IN_QID_OFST_MAXNUM);
+
 	rxqs = kmalloc(count * sizeof(*rxqs), GFP_KERNEL);
 	if (rxqs == NULL)
 		return VFDI_RC_ENOMEM;