[PATCH net v3 3/4] netdevsim: support devmem RX and TX bindings

[Mina Almasry <almasrymina@google.com>]

Set a 64-bit DMA mask on nsim_bus_dev, enable NETMEM_TX_DMA on the
netdevsim net_device, and configure page_pool instances with
PP_FLAG_ALLOW_UNREADABLE_NETMEM and queue_idx, plus PP_FLAG_DMA_MAP |
PP_FLAG_DMA_SYNC_DEV when CONFIG_HAS_DMA is set, so devmem bind-rx and
bind-tx netlink operations can be tested against netdevsim in software
selftests.

The pp_hold debugfs file allocates pages from the queue 0 page pool, so
refuse it when that pool is backed by a memory provider, and take the
netdev instance lock there so a concurrent bind-rx cannot swap the pool
in between. The software PSP path checksums the payload when the peer
does not decapsulate, so drop unreadable skbs there.

Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Kaifeng Wang <kaifengw@google.com>
Assisted-by: LLM
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
---
v3:
- Only request page pool DMA mapping when CONFIG_HAS_DMA is set
  (Sashiko).
- Refuse pp_hold on a page pool backed by a memory provider, under the
  netdev instance lock (Sashiko).
- Drop unreadable skbs in the software PSP path when it would have to
  checksum the payload (Sashiko).
---
 drivers/net/netdevsim/bus.c    |  1 +
 drivers/net/netdevsim/netdev.c | 27 +++++++++++++++++++++------
 drivers/net/netdevsim/psp.c    |  5 +++++
 3 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c
index 5c55c308487b4..f87f5e037b6fb 100644
--- a/drivers/net/netdevsim/bus.c
+++ b/drivers/net/netdevsim/bus.c
@@ -462,6 +462,7 @@ nsim_bus_dev_new(unsigned int id, unsigned int port_count, unsigned int num_queu
 	nsim_bus_dev->port_count = port_count;
 	nsim_bus_dev->num_queues = num_queues;
 	nsim_bus_dev->initial_net = current->nsproxy->net_ns;
+	dma_coerce_mask_and_coherent(&nsim_bus_dev->dev, DMA_BIT_MASK(64));
 	/* Disallow using nsim_bus_dev */
 	smp_store_release(&nsim_bus_dev->init, false);
 
diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index b4a99f3ceac60..357ea9e5623b3 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -414,19 +414,27 @@ static int nsim_poll(struct napi_struct *napi, int budget)
 	return done;
 }
 
-static int nsim_create_page_pool(struct page_pool **p, struct napi_struct *napi)
+static int nsim_create_page_pool(struct net_device *dev, struct page_pool **p,
+				 struct napi_struct *napi, int idx)
 {
+	struct netdevsim *ns = netdev_priv(dev);
 	struct page_pool_params params = {
 		.order = 0,
 		.pool_size = NSIM_RING_SIZE,
+		.flags = PP_FLAG_ALLOW_UNREADABLE_NETMEM,
+		.max_len = PAGE_SIZE,
 		.nid = NUMA_NO_NODE,
-		.dev = &napi->dev->dev,
+		.dev = &ns->nsim_bus_dev->dev,
 		.napi = napi,
 		.dma_dir = DMA_BIDIRECTIONAL,
-		.netdev = napi->dev,
+		.netdev = dev,
+		.queue_idx = idx,
 	};
 	struct page_pool *pool;
 
+	if (IS_ENABLED(CONFIG_HAS_DMA))
+		params.flags |= PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV;
+
 	pool = page_pool_create(&params);
 	if (IS_ERR(pool))
 		return PTR_ERR(pool);
@@ -450,7 +458,7 @@ static int nsim_init_napi(struct netdevsim *ns)
 	for (i = 0; i < dev->num_rx_queues; i++) {
 		rq = ns->rq[i];
 
-		err = nsim_create_page_pool(&rq->page_pool, &rq->napi);
+		err = nsim_create_page_pool(dev, &rq->page_pool, &rq->napi, i);
 		if (err)
 			goto err_pp_destroy;
 	}
@@ -762,14 +770,16 @@ nsim_queue_mem_alloc(struct net_device *dev,
 	if (ns->rq_reset_mode == 1) {
 		if (!netif_running(ns->netdev))
 			return -ENETDOWN;
-		return nsim_create_page_pool(&qmem->pp, &ns->rq[idx]->napi);
+		return nsim_create_page_pool(dev, &qmem->pp,
+					     &ns->rq[idx]->napi, idx);
 	}
 
 	qmem->rq = nsim_queue_alloc();
 	if (!qmem->rq)
 		return -ENOMEM;
 
-	err = nsim_create_page_pool(&qmem->rq->page_pool, &qmem->rq->napi);
+	err = nsim_create_page_pool(dev, &qmem->rq->page_pool, &qmem->rq->napi,
+				    idx);
 	if (err)
 		goto err_free;
 
@@ -929,12 +939,15 @@ nsim_pp_hold_write(struct file *file, const char __user *data,
 		return ret;
 
 	rtnl_lock();
+	netdev_lock(ns->netdev);
 	ret = count;
 	if (val == !!ns->page)
 		goto exit;
 
 	if (!netif_running(ns->netdev) && val) {
 		ret = -ENETDOWN;
+	} else if (val && page_pool_is_unreadable(ns->rq[0]->page_pool)) {
+		ret = -EOPNOTSUPP;
 	} else if (val) {
 		ns->page = page_pool_dev_alloc_pages(ns->rq[0]->page_pool);
 		if (!ns->page)
@@ -946,6 +959,7 @@ nsim_pp_hold_write(struct file *file, const char __user *data,
 	}
 
 exit:
+	netdev_unlock(ns->netdev);
 	rtnl_unlock();
 	return ret;
 }
@@ -1051,6 +1065,7 @@ static int nsim_init_netdevsim(struct netdevsim *ns)
 	ns->netdev->netdev_ops = &nsim_netdev_ops;
 	ns->netdev->stat_ops = &nsim_stat_ops;
 	ns->netdev->queue_mgmt_ops = &nsim_queue_mgmt_ops;
+	ns->netdev->netmem_tx = NETMEM_TX_DMA;
 	netdev_lockdep_set_classes(ns->netdev);
 
 	err = nsim_udp_tunnels_info_create(ns->nsim_dev, ns->netdev);
diff --git a/drivers/net/netdevsim/psp.c b/drivers/net/netdevsim/psp.c
index 6b3532b5e360d..908cc0d391dc6 100644
--- a/drivers/net/netdevsim/psp.c
+++ b/drivers/net/netdevsim/psp.c
@@ -86,6 +86,11 @@ nsim_do_psp(struct sk_buff *skb, struct netdevsim *ns,
 		__wsum csum;
 		int udplen;
 
+		if (!skb_frags_readable(skb)) {
+			rc = SKB_DROP_REASON_PSP_OUTPUT;
+			goto out_unlock;
+		}
+
 		/* Do not decapsulate. Receive the skb with the udp and psp
 		 * headers still there as if this is a normal udp packet.
 		 * psp_dev_encapsulate() sets udp checksum to 0, so we need to
-- 
2.56.0.176.g3575e65682-goog